Plasma immersion ion implantation process

ABSTRACT

A method of processing a workpiece includes placing the workpiece on a workpiece support pedestal in a main chamber with a gas distribution showerhead, introducing a process gas into a remote plasma source chamber and generating a plasma in the remote plasma source chamber, transporting plasma-generated species from the remote plasma source chamber to the gas distribution showerhead so as to distribute the plasma-generated species into the main chamber through the gas distribution showerhead, and applying plasma RF power into the main chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.10/929,104, filed Aug. 26, 2004, now abandoned, entitled GASLESS HIGHVOLTAGE HIGH CONTACT FORCE WAFER CONTACT-COOLING ELECTROSTATIC CHUCK byDouglas A. Buchberger, Jr., et al. This application is also acontinuation-in-part of U.S. application Ser. No. 10/838,052, filed May3, 2004 entitled LOW TEMPERATURE CVD PROCESS WITH CONFORMALITY, STRESSAND COMPOSITION by Hiroji Hanawa, et al., now issued as U.S. Pat. No.7,223,676, which is a continuation-in-part of U.S. application Ser. No.10/786,410, filed Feb. 24, 2004 entitled FABRICATION OFSILICON-ON-INSULATOR STRUCTURE USING PLASMA IMMERSION ION IMPLANTATIONby Dan Maydan, et al., now issued as U.S. Pat. No. 6,893,907, which is acontinuation-in-part of U.S. application Ser. No. 10/646,533, filed Aug.22, 2003 entitled PLASMA IMMERSION ION IMPLANTATION PROCESS USING APLASMA SOURCE HAVING LOW DISSOCIATION AND LOW MINIMUM PLASMA VOLTAGE,which is a continuation-in-part of U.S. application Ser. No. 10/164,327,filed Jun. 5, 2002 entitled EXTERNALLY EXCITED TORROIDAL PLASMA SOURCEWITH MAGNETIC CONTROL OF ION DISTRIBUTION by Kenneth Collins et al., nowissued as U.S. Pat. No. 6,939,434, which is a continuation-in-part ofU.S. application Ser. No. 09/636,435, filed Aug. 11, 2000 entitledEXTERNALLY EXCITED MULTIPLE TORROIDAL PLASMA SOURCE by Hiroji Hanawa etal., now issued as U.S. Pat. No. 6,494,986 B1, all of which applicationslisted above are assigned to the present assignee.

BACKGROUND OF THE INVENTION

The present invention concerns plasma immersion ion implantationreactors of the type disclosed in the above-referenced parentapplications in which a pair of external reentrant conduits define apair of transverse toroidal paths in which RF oscillating plasmacurrents are maintained by RF source power applied to the interiors ofthe conduits. A plasma immersion ion implantation process carried out insuch a reactor typically requires that the semiconductor wafer becleaned or otherwise prepared beforehand. Such a cleaning process can becarried out very rapidly using a plasma process, but this can leave thewafer surface very rough, leading to inferior results. For example, arough surface that is ion implanted with a dopant material can have anexcessive sheet resistance. Deposition of an epitaxial layer (by aplasma enhanced chemical vapor deposition process, for example) on arough surface can result in a low quality deposited layer that is lesscrystalline and more amorphous. Such problems can be avoided by carryingout the wafer cleaning process using a cleaning gas without employingany plasma. This approach leaves the smoothest wafer surface but can beunacceptably slow, and in many cases should be carried out at asufficiently high temperature to activate the gas species. Such a hightemperature can exceed the wafer process thermal budget. In order toclean the wafer faster but avoid surface damage of the type encounteredwith plasma cleaning processes and high temperatures of the non-plasmacleaning process, the cleaning gas can be dissociated into reactiveneutrals. This latter approach would be ideal, except that it requires aremote plasma source (RPS) reactor that furnishes the reactive neutralsor radicals to the main chamber. The problem is that the external feedfrom the RPS chamber to the main chamber holding the wafer does notprovide a uniform distribution of the neutrals or radicals over thewafer surface, so that the wafer cannot be cleaned uniformly. Typically,the radicals or neutrals from the RPS chamber are fed to a side port ofthe main chamber, leading to the non-uniformity. What is needed is a wayof cleaning a wafer rapidly and uniformly without impairing wafersurface quality and without having to employ very high temperatures.

A plasma immersion ion implantation reactor must be cleanedperiodically. In some cases, such periodic cleaning is required to avoidexcessive metal contamination of the wafer process. The best results(lowest contamination) are obtained when the chamber is cleaned everytime a wafer is processed. This is only practical if the cleaningprocess is less than the time required to perform the wafer process, inorder to avoid an excess loss of productivity. The fastest processes forcleaning the chamber interior are plasma cleaning processes, and thesecan meet the productivity goals. Unfortunately, plasma cleaning processare so fast that they tend to consume a relatively large fraction of thechamber surfaces and elements (such as process kits), and therefore areextremely costly insofar as they require frequent replacement of chamberinterior parts and materials. The minimum consumption of chamberinterior elements for a thorough cleaning is obtained using cleaninggases without a plasma, but this approach is too time-consuming. Thebest compromise is obtained by employing dissociated cleaning gases. Theproblem with this approach is that distribution within the main chamberof the dissociated cleaning gases from an external remote plasma source(RPS) chamber is non-uniform, so that the main chamber cannot be cleaneduniformly. This is because the external feed from the RPS chamber to themain chamber does not provide a uniform distribution of the neutrals orradicals within the main chamber. Typically, the dissociated gases fromthe RPS chamber are fed to a side port of the main chamber.

One problem encountered in plasma immersion ion implantation is that thedopant-containing process gas can sometimes form a film on the surfacebeing implanted that can block the implantation or distort the implantdepth profile from the desired one. Such an unwanted film can, in somecases, distort the ion implantation depth profile (or render itdifficult to control during implantation), so that the resulting depthprofile may not be ideal. Another problem is that the ion bombardmentcan etch away the surface being implanted, removing much of theimplanted ions and thereby attenuating the desired effects of theimplantation process. In a dopant implantation process in asemiconductor layer, this problem manifests itself as a high sheetresistance.

Another problem that can arise in any plasma process is contamination onthe wafer backside that degrades subsequent wafer processing steps. Ourexperience has led us to believe that such backside contamination arisesfrom contact between the wafer backside and the electrostatic chuck(ESC) top surface and the flexing of the wafer during wafer chucking anddechucking. Metallic contamination occurs because in many cases theinsulating layer on the ESC surface is a metal containing compound suchas AlN. AlN particles scraped onto the wafer backside from the ESC canbe dissociated in later plasma process steps to free the Al species andform metallic contamination, which can degrade process performance.There is a need to prevent such contamination without creating otherburdens on the process.

SUMMARY OF THE INVENTION

One method of performing plasma immersion ion implantation on aworkpiece in a plasma reactor chamber includes initially depositing aseasoning film on the interior surfaces of the plasma reactor chamberbefore the workpiece is introduced, by introducing a seasoning filmprecursor gas into the chamber and generating a plasma within thechamber, performing plasma immersion ion implantation on the workpieceby introducing an implant species precursor gas into the chamber andgenerating a plasma, and then removing the workpiece from the chamberand removing the seasoning film from the chamber interior surfaces. Inone embodiment, the implant species precursor gas comprises a fluorideof a dopant species, the seasoning film precursor gas comprises afluorocarbon gas and the seasoning film comprises a fluorocarbonpolymer. In another embodiment, the implant species precursor gascomprises a hydride of a dopant species, the seasoning film precursorgas comprises a hydrocarbon gas and the seasoning film comprises afluorocarbon polymer. In a further embodiment, the implant speciesprecursor gas comprises nitrogen gas, the seasoning film precursor gascomprises nitrogen and a hydride of silicon and the seasoning filmcomprises silicon nitride. In yet another embodiment, the implantprecursor species comprises fluorine, the seasoning film precursor gascomprises a fluorocarbon gas and the seasoning film comprises afluorocarbon polymer.

A method of processing a workpiece in a plasma reactor chamber includesinitially depositing an elastic cushioning film on the wafer-supportsurface of a wafer support within the chamber before introduction of theworkpiece, by introducing an elastic material precursor gas into thechamber and generating a plasma within the chamber, placing theworkpiece on the elastic cushioning film a workpiece support in thechamber, and introducing a workpiece processing gas into the chamber andprocessing the workpiece in the chamber. This is followed by removingthe workpiece from the chamber and removing the elastic cushioning filmfrom the wafer support. The elastic material precursor gas can be one of(a) a fluorocarbon gas, (b) a hydrocarbon gas, (c) a fluoro-hydrocarbongas, and wherein the elastic cushioning layer comprises a polymer.Preferably, the method includes providing a generally uninterruptedcontinuous polished surface as the workpiece support surface of thewafer support. In this case, the temperature of the workpiece can becontrolled by applying a sufficiently large electrostaticworkpiece-clamping voltage to attain a desired workpiece temperature.

In another aspect, a multimode plasma reactor includes a main chamberhaving an enclosure comprising a side wall and a ceiling, the ceilingcomprising a gas distribution showerhead, a wafer support in the mainchamber facing the ceiling, a pair of openings through the enclosure ongenerally opposite sides of the chamber, a first hollow reentrantconduit having two ends coupled to the pair of openings and defining afirst closed reentrant path through the first conduit and across aprocess region between the wafer support and the showerhead, thetoroidal path surrounding the ceiling, a first plasma source powerapplicator facing a section of the first reentrant conduit. The reactorfurther includes a remote plasma source chamber having a process gasinput, a radical supply conduit coupled between the remote plasma sourcechamber and the gas distribution showerhead of the main chamber, a firstgas supply feed line coupled to the remote plasma source chamber, asecond gas supply feed line coupled to the gas distribution showerheadof the main chamber, and a gas supply coupled to at least one of the gassupply feed lines. The main chamber can further include main chamber gasinjectors, the reactor further including a third gas supply feed linecoupled to the gas injectors.

The wafer support can be a high contact force electrostatic chuck havinga flat polished workpiece contact surface, in which case a workpiecetemperature controller governs a wafer clamping voltage of theelectrostatic chuck. The bias source can be one of (a) an RF source, (b)a D.C. source. The plasma source power applicator can include a toroidalcore of a magnetic material surrounding a section of the reentrantconduit and a conductor wound around the core and coupled to the RFsource power generator.

A method of processing a workpiece in a plasma reactor chamber having agas distribution showerhead facing a workpiece support and defining aprocess region therebetween, includes initially depositing a seasoningfilm on interior surfaces of the chamber by introducing a seasoning filmprecursor gas into the reactor chamber and generating an oscillatingplasma current in a toroidal path that passes through the process regionand through an external reentrant hollow conduit. The method furtherproceeds with the steps of introducing the workpiece into the reactorchamber and processing it by introducing a workpiece process precursorgas into a remote plasma source chamber, generating a plasma in theremote plasma source chamber, and delivering radicals from the plasma inthe remote plasma source chamber to the gas distribution showerhead ofthe plasma reactor chamber whereby to distribute the radicals in theprocess region over the workpiece. These steps are preferably followedby removing the workpiece from the reactor chamber and then removing theseasoning film from the chamber interior surfaces by introducing aseasoning film etchant precursor gas into the remote plasma sourcechamber, generating a plasma in the remote source plasma chamber, anddelivering radicals from the plasma in the remote source plasma chamberto the gas distribution showerhead of the plasma reactor chamber wherebyto distribute the radicals in the plasma reactor chamber.

A method of processing a workpiece in a plasma reactor chamber having agas distribution showerhead facing a workpiece support and defining aprocess region therebetween, includes initially depositing a seasoningfilm on interior surfaces of the chamber by introducing a seasoning filmprecursor gas into the reactor chamber and generating an oscillatingplasma current in a toroidal path that passes through the process regionand through an external reentrant hollow conduit. The method furtherproceeds with the steps of introducing the workpiece into the reactorchamber and processing it by introducing a non-reactive gas into aremote plasma source chamber, generating a plasma in the remote plasmasource chamber, delivering excited non-reactive gas from the plasma inthe remote plasma source chamber to the gas distribution showerhead ofthe plasma reactor chamber whereby to distribute the excitednon-reactive gas in the process region over the workpiece, andintroducing into the plasma reactor chamber a workpiece process gascomprising reactive species. Preferably, the plasma in the remote plasmasource chamber comprises excited gas having sufficient energy todissociate at least a portion of the workpiece process gas in the plasmareactor chamber. These steps are preferably followed by removing theworkpiece from the reactor chamber and then removing the seasoning filmfrom the chamber interior surfaces by introducing a seasoning filmetchant precursor gas into the remote plasma source chamber, generatinga plasma in the remote source plasma chamber, and delivering radicalsfrom the plasma in the remote source plasma chamber to the gasdistribution showerhead of the plasma reactor chamber whereby todistribute the radicals in the plasma reactor chamber.

A method of processing a workpiece in a plasma reactor chamber having agas distribution showerhead facing a workpiece support and defining aprocess region therebetween, and having a reentrant hollow conduitproviding a toroidal path extending across the process region andthrough the reentrant hollow conduit, includes introducing a workpieceprocess reactive gas into a remote plasma source chamber, generating aplasma in the remote plasma source chamber, delivering reactive radicalsfrom the plasma in the remote plasma source chamber to the gasdistribution showerhead of the plasma reactor chamber whereby todistribute the radicals in the process region over the workpiece, andgenerating an oscillating plasma current in the toroidal path. Theoscillating plasma current can be generated by applying RF plasma sourcepower to an interior portion of the conduit. The method can furtherinclude coupling a bias source to the workpiece support.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut-away side view of a plasma reactor for processing asemiconductor wafer that includes the wafer contact-coolingelectrostatic chuck.

FIG. 2 is a cross-sectional side view of the wafer contact-coolingelectrostatic chuck.

FIGS. 3 and 4 are top cross-sectional views of different layers of thewafer contact-cooling electrostatic chuck.

FIG. 5 illustrates an alternative implementation of the chuck of FIG. 2.

FIG. 6 illustrates the behavior of the heat transfer coefficient in theembodiment of FIG. 2 or 5 as a function of chucking voltage.

FIG. 7 illustrates the behavior of the heat transfer coefficient in theembodiment of FIG. 2 or 5 as a function of puck surface finish.

FIG. 8 illustrates the behavior of the heat transfer coefficient in theembodiment of FIG. 2 or 5 as a function of the proportion of the pucksurface that is smooth.

FIGS. 9A, 9B and 9C illustrate the wafer curvature for differentmagnitudes of the chucking voltage.

FIG. 10 illustrates the chucking voltage over time corresponding to thesequence of FIGS. 9A through 9C.

FIGS. 11A and 11B are cut-away side and top views, respectively, of atoroidal source plasma reactor embodying the present invention.

FIG. 12 illustrates a seasoning film deposited on a chamber interiorwall surface of the reactor of FIG. 11A and a cushioning film depositedon the wafer support surface of the electrostatic chuck of the reactorof FIG. 11A.

FIG. 13 is a block flow diagram illustrating a plasma immersion ionimplantation process.

FIG. 14 illustrates a wafer processing method employing a pre-processchamber seasoning step for low contamination.

FIG. 15 illustrates a wafer processing method in which radicals ordissociated neutrals are introduced from a remote plasma source into themain plasma chamber of FIG. 11A through the gas distribution showerhead.

FIGS. 16 and 17 illustrate wafer processes performed by the multimodereactor of FIG. 11A that use both the RPS reactor source power and themain chamber source power simultaneously.

FIG. 18 illustrates a process that can be carried out in any plasmareactor for eliminating or reducing contamination.

DETAILED DESCRIPTION OF THE INVENTION

High Contact Force Gasless Electrostatic Chuck:

FIGS. 1 through 4 depict a plasma reactor with the wafer contact-coolingelectrostatic chuck in accordance with certain embodiments of theinvention. FIG. 1 is a cut-away side view of a plasma reactor forprocessing a semiconductor reactor that includes the wafercontact-cooling electrostatic chuck. FIG. 2 is a cross-sectional sideview of the wafer contact-cooling electrostatic chuck. FIGS. 3 and 4 aretop cross-sectional views of different layers of the wafercontact-cooling electrostatic chuck. In FIG. 1, the plasma reactor has acylindrical side wall 10, a ceiling 12 and a wafer contact-coolingelectrostatic chuck 14. A pumping annulus 16 is defined between thechuck 14 and the sidewall 10. While the wafer contact-coolingelectrostatic chuck 14 may be used in any type of plasma reactor orother reactor (such as thermal process reactor), the reactor in theexample of FIG. 1 is of the type in which process gases can beintroduced through a gas distribution plate 18 (or “showerhead”) forminga large portion of the ceiling 12. Alternatively, the reactor could havegas distribution inlets 20 (dashed lines) that are separate from theceiling 12. While the wafer contact-cooling electrostatic chuck 14 maybe employed in conjunction with any plasma source (such as aninductively coupled RF plasma source, a capacitively coupled RF plasmasource or a microwave plasma source), the reactor in the example of FIG.1 has a reentrant RF torroidal plasma source consisting of an externalreentrant tube 22 coupled to the interior of the reactor throughopposite sides of the sidewall 10 (or, through openings in the ceiling12 not shown in FIG. 1). An insulating ring 23 provides a D.C. breakalong the reentrant tube 22. The torroidal plasma source furtherincludes an RF power applicator 24 that may include a magneticallypermeable torroidal core 26 surrounding an annular portion of thereentrant tube 22, a conductive coil 28 wound around a portion of thecore 26 and an RF plasma source power generator 30 coupled to theconductive coil through an optional impedance match circuit 32. Aprocess gas supply 34 is coupled to the gas distribution plate 18 (or tothe gas injectors 20). A semiconductor wafer or workpiece 40 is placedon top of the chuck 14. A processing region 42 is defined between thewafer 40 and the ceiling 12 (including the gas distribution plate 18). Atorroidal plasma current oscillates at the frequency of the RF plasmasource power generator 30 along a closed torroidal path extendingthrough the reentrant tube 22 and the processing region 42.

RF bias power is applied to the chuck 14 by an RF bias power generator44 through an impedance match circuit 46. A D.C. chucking voltage isapplied to the chuck 14 from a chucking voltage source 48 isolated fromthe RF bias power generator 44 by an isolation capacitor 50. The RFpower delivered to the wafer 40 from the RF bias power generator 44 canheat the wafer 40 to temperatures beyond 400 degrees C., depending uponthe level and duration of the applied RF plasma bias power from thegenerator 44. It is believed that about 80% or more of the RF power fromthe bias power generator 44 is dissipated as heat in the wafer 40.

In other implementations, there may be little or no bias delivered bythe bias power generator 44 (or there may be no bias power generator),in which case the wafer 40 is heated (indirectly) by power from thesource power generator 30 via interaction between the wafer 40 and theplasma in the chamber. This interaction can include bombardment of thewafer by plasma ions, electrons and neutrals, with wafer heating arisingfrom the kinetic energy of the ions, electrons and neutrals, as well aselectrical effects arising from the interaction of the charged particleswith electric fields in the vicinity of the wafer, as is well-known inthe art. The wafer may be heated by radiation emitted by plasma species,such as ultraviolet, visible or infrared radiation emitted by excitedatomic or molecular species (ions or neutrals) during relaxation, as iswell known in the art. The wafer may be heated by other means, such asby hot surfaces in or adjacent the process chamber, by thermalradiation, convection or conduction, as is well known in the art. Thus,the wafer 40 is heated directly by RF power from the bias powergenerator 44 or indirectly (via wafer-plasma interaction) by RF powerfrom the source power generator 30.

Conventionally, the wafer temperature was regulated to avoid overheatingby providing coolant gas at a selected pressure between the wafer 40 andthe chuck 14 and removing heat from the gas. Such gas introductionrequires open gas channels in the chuck surface on which the wafer ismounted. The presence of such open coolant gas channels in the chucksurface creates two problems. First, the RF bias power applied to thechuck can cause the gas to break down in the channels. This problem issolved by either limiting the coolant gas pressure (which reduces theheat transfer from the wafer) or by limiting the RF bias voltage, e.g.,to below 1 kV (which can negatively impact plasma processing). A secondproblem is that the many sharp edges defining the open gas channels inthe chuck surface lead to contamination, either by the breaking off ofmaterial forming the sharp edges or by arcing near those edges, or byscratching of the wafer backside. A related problem is that inapplications requiring very high RF bias power levels, the coolant gasbreaks down (preventing operation) and the coolant gas system may havean insufficient heat transfer coefficient for the high heat load on thewafer.

The electrostatic chuck 14 of FIG. 2 is a wafer contact-coolingelectrostatic chuck in which the portion of the chuck contacting thewafer is cooled. The wafer contact-cooling electrostatic chuck 14requires no gas cooling source nor internal gas coolant passages to keepthe wafer cool and remove heat from the wafer. Instead, the heat isremoved from the wafer at a rate which limits the maximum wafertemperature or the time rate of rise of the wafer temperature duringplasma processing, by cooling the chuck 14 itself while maintainingdirect high-force contact between the wafer 40 and the chuck 14, as willnow be described. Alternatively, the chucking voltage may be variedduring wafer processing to vary the selected heat transfer coefficientin order to control wafer temperature to a target value. This latterfeature may be carried out by monitoring the wafer temperature andvarying the chuck voltage so as to minimize the difference between themeasured wafer temperature and a target temperature. As the measuredwafer temperature rises above a maximum target temperature, the chuckingvoltage is increased, and as the measured wafer temperature falls belowa target minimum temperature, the chucking voltage may be decreased.Moreover, the high-force contact cooling of the wafer is able to controlwafer temperature even at very high RF bias power levels.

Referring to FIG. 2, the chuck 14 has a top layer 60, referred to as apuck, consisting of insulative or semi-insulative material, such asaluminum nitride or aluminum oxide, which may be doped with othermaterials to control its electrical and thermal properties. A metal(molybdenum, for example) wire mesh or metal layer 62 inside of the puck60 forms a cathode (or electrode) to which the chucking voltage isapplied. The puck 60 may be formed as a ceramic. Or, it may be formed byplasma or physical deposition processes, or chemical vapor depositionprocess or plasma or flame spray coating or other method. It issupported on a metal layer 64, preferably consisting of a metal having ahigh thermal conductivity, such as aluminum. The metal layer 64 rests ona highly insulative layer 66 whose thickness, dielectric constant anddielectric loss tangent are chosen to provide the chuck 14 with selectedRF characteristics (e.g., capacitance, loss resistance) compatible withthe reactor design and process requirements. A metal base layer 68 isconnected to ground. The wafer 40 is held on the chuck 14 by applying aD.C. voltage from the chucking voltage source 48 to the electrode 62.The application of voltage across the insulator layer 60 polarizes theinsulator 60 and induces an opposite (attractive) image charge in thebottom surface of the wafer 40. In the case of a semi-insulator layer60, in addition to inducing image charge in the bottom surface of thewafer, charge from the electrode 62 migrates through the semi-insulatorlayer 60 to accumulate very close to the top surface of thesemi-insulator layer 60, for a minimum gap between the charge and theoverlying wafer 40. (The term “semi-insulator” is discussed below.) Thisinduces an opposite (attractive) image charge in the bottom surface ofthe wafer 40. The effective gap between the two opposing charge layersis so minimal as a result of the upward charge migration in theinsulator layer 60 that the attractive force between the chuck and thewafer 40 is very large for a relatively small applied chucking voltage.For example, a chucking voltage of only 300 volts D.C. on the electrode62 produces a chucking force across the wafer 40 equivalent to apressure of about 100 Torr. The puck semi-insulator layer 60 thereforeis formed of a material having a desired charge mobility, so that thematerial is not a perfect insulator (hence, the term “semi-insulator”).This semi-insulator material, although not a perfect insulator, may alsonot be a typical semiconductor, in some cases. In any case, the chargeinduced by the chucking voltage on the electrode 62 is mobile in thesemi-insulator material of the puck layer 60, and therefore it may besaid that the puck semi-insulator layer 60 is formed of a “chargemobile” material. One example of a material suitable for the pucksemi-insulator or charge mobile layer 60 is aluminum nitride. Anotherexample is aluminum oxide, which may optionally be doped to increasecharge mobility. For example, the dopant material may be titaniumdioxide.

RF bias power from the RF bias power generator 44 may be applied to theelectrode 62 or, alternatively, to the metal layer 64 for RF couplingthrough the semi-insulative puck layer 60.

A very high heat transfer coefficient between the wafer 40 and the puck60 is realized by maintaining a very high chucking force. A suitablerange for this force depends upon the anticipated heat loading of thewafer, and will be discussed later in this specification. The heattransfer coefficient (having units of Watts/m²° K or heat flux densityfor a given temperature difference) of the wafer-to-puck contactingsurfaces is adequate to remove heat at the rate heat is deposited on thewafer. Specifically, the heat transfer coefficient is adequate becauseduring plasma processing it either limits the wafer temperature below aspecified maximum temperature or limits the time rate of rise of thewafer temperature below a maximum rate of rise. The maximum wafertemperature may be selected to be anywhere in a practical range from onthe order to 100 degrees C. or higher, depending upon the heat load. Themaximum rate of heat rise during processing may be anywhere in a rangefrom 3 to 20 degrees per second. Specific examples may be 20 degrees persecond, or 10 degrees per second or 3 degrees per second. By comparison,if the wafer is uncooled, the rate of heat rise may be 86.7 degrees persecond in the case of a typical 300 mm silicon wafer with a heat load of7500 Watts, 80% of which is absorbed by the wafer. Thus, the rate oftemperature rise is reduced to one-fourth of the uncooled rate of heatrise in one embodiment of the invention.

Such performance is accomplished, first, by maintaining the puck at asufficiently low temperature (for example, about 80° C. below the targetwafer temperature), and second, by providing the top surface of the puck60 with a sufficiently smooth finish (e.g., on the order of ten's ofmicro-inches RMS deviation, or preferably on the order of micro-inchesRMS deviation). For this purpose, the top surface 60 a of the puck 60can be highly polished to a finish on the order of about 2 micro-inchesRMS deviation, for example. Furthermore, heat is removed from the puck60 by cooling the metal layer 64. For this reason, internal coolantpassages 70 are provided within the metal layer 64 coupled to a coolantpump 72 and heat sink or cooling source 74. In an alternativeembodiment, the internal cooling passages 70 may extend into the puck 60or adjacent its back surface in addition or instead of extending throughthe metal layer 64. In any case, the coolant passages 70 are thermallycoupled to the puck 60, either directly or through the metal layer 64,and are for cooling the puck 60. The coolant liquid circulating throughthe internal passages 70 can be water, ethylene glycol or a mixture, forexample. Alternatively, the coolant may be a perfluorinated heattransfer liquid such as “fluorinert” (made by 3M company). Unlike theinternal gas coolant passages of conventional chucks, this featurepresents little or no risk of arcing in the presence of high RF biaspower applied to the chuck 14 by the RF bias power generator 44.

The chucking voltage required to attain a particular heat transfercoefficient is increased if an insulating (oxide or nitride, forexample) layer is added to the wafer backside. Therefore, the chuckingvoltage must be determined empirically each time a new batch of wafersis to be processed. This is inconvenient and reduces productivity. Oneway around this problem is to mask the difference between wafers withand without a backside oxide layer. The difference is masked by adding athin insulating layer 60 b on the top puck surface 60 a. The presence ofsuch a thin insulating layer increases the requisite chucking voltage toreach a particular heat transfer coefficient value. In this way, thechucking voltage required remains at least nearly the same whether ornot the wafer backside has an insulating layer. The thin insulatinglayer 60 b may be formed on the top puck surface 60 a during initialpuck fabrication or may be formed within the process chamber.

One advantage of such contact-cooling of the wafer over the conventionalmethod employing a coolant gas is that the thermal transfer efficiencybetween the coolant gas and each of the two surfaces (i.e., the pucksurface and the wafer bottom surface) is very limited, in accordancewith the thermal accommodation coefficient of the gas with the materialsof the two surfaces. The heat transfer rate is attenuated by the productof the gas-to-wafer thermal accommodation coefficient and thegas-to-puck thermal accommodation coefficient. If both coefficients areabout 0.5 (as a high rough estimate), then the wafer-gas-puck thermalconductance is attenuated by a factor of about 0.25. In contrast, thecontact-cooling thermal conductance in the present invention hasvirtually no such attenuation, the thermal accommodation coefficientbeing in effect unity for the chuck 14 of FIGS. 1-4. Therefore, thecontact cooling electrostatic chuck 14 can outperform conventionalelectrostatic chucks (i.e., electrostatic chucks that that employ gascooling) by a factor of about four (or more) with sufficiently highattractive electrostatic force between wafer and puck. We have observedin preliminary tests an improvement of about a factor of three.

The heat transfer coefficient between the wafer 40 and the puck 60 inthe wafer contact-cooling electrostatic chuck 14 is affected by the pucktop surface finish and the chucking force. These parameters can beadjusted to achieve the requisite heat transfer coefficient for aparticular environment. An important environmental factor determiningthe required heat transfer coefficient is the applied RF bias powerlevel. It is believed that at least 80% of the RF bias power from thebias generator 44 is dissipated as heat in the wafer 40. Therefore, forexample, if the RF bias power level is 7500 Watts and 80% of the RF biaspower from the bias generator 44 is dissipated as heat in the wafer 40,if the wafer area is 706 cm² (300 mm diameter wafer) and if a 80 degreesC. temperature difference is allowed between the wafer 40 and the puck60, then the required heat transfer coefficient is h=7500×80% Watts/(706cm²×80 degrees K), which is 1071 Watts/m²° K. For greater RF bias powerlevels, the heat transfer coefficient can be increased by augmenting anyone or both of the foregoing factors, namely the temperature drop acrossthe puck, the chucking force or the smoothness of the puck surface. Sucha high heat transfer coefficient, rarely attained in conventionalelectrostatic chucks, is readily attained in the electrostatic chuck 14of FIG. 2 by applying a sufficiently high chucking voltage, on the orderof 1 kV, for example.

In addition, the heat transfer is improved by providing more pucksurface area available for direct contact with the wafer backside. In aconventional chuck, the puck surface available for wafer contact isgreatly reduced by the presence of open coolant gas channels machined,ground or otherwise formed in the puck surface. These channels occupy alarge percentage of the puck surface. In the puck 60 of FIG. 3, the onlyinterruptions in the surface are three small lift pin holes 80 a, 80 b,80 c. Therefore, the percentage of the puck cross-sectional area (3.14r²) based upon the puck radius (r) that is available for direct wafercontact is significantly higher (i.e., 30%-95% of the totalcross-sectional area of the chuck), thus maximizing the wafer-puck heattransfer coefficient. A related feature is that the surface contact areabetween the puck 60 and the cooled metal plate 64 is likewise a veryhigh percentage of the total cross-sectional area of the plate 64. Thisis because, as shown in FIG. 4, the plate 64 has a top surfaceinterrupted by corresponding lift pin holes 80 a, 80 b, 80 c and centerelectrical conduit hole 82. Its bottom surface has, in addition, coolantingress and egress holes 84 a, 84 b.

FIG. 5 illustrates an alternative implementation of the wafercontact-cooling electrostatic chuck of FIG. 2, in which the insulatorlayer 66 and the bottom metal layer 68 can be eliminated, while the puck60 is modified to have two layers, an upper semi-insulative layer 60-1(e.g., lower resistivity aluminum nitride) and a lower highly insulative(e.g., higher resistivity aluminum nitride) layer 60-2. In thisimplementation, the overall thickness of the puck 60 is greater, becausethe lower insulator layer 60-2 must be sufficiently thick to provide acertain RF capacitance selected by the system designer (requirement istypically to be less than some maximum value). The top puck layer 60-1of FIG. 5 may be nearly identical to the puck 60 of FIG. 2.

FIG. 6 is a graph illustrating the behavior of the heat transfercoefficient, h (vertical axis), as a function of the chucking voltageapplied by the chucking voltage source 48 (horizontal axis). FIG. 6shows that remarkably high heat transfer coefficient values (1000 to3000 Watts/m²° K are obtained within a relatively modest range ofchucking voltages (1000 to 2000 Volts D.C.).

FIG. 7 is a graph illustrating the behavior of the heat transfercoefficient, h (vertical axis), as a function of the surface finish ofthe puck top surface 60 a. FIG. 7 shows that robust heat transfercoefficient values (1000 to 3000 Watts/m²° K) are obtained within apractical range of surface finish values (1 to 3 micro-inches RMS).

FIG. 8 is a graph illustrating the behavior of the heat transfercoefficient, h (vertical axis), as a function of the percentage of thepuck top surface 60 a that is flat (e.g., not taken up by surfacechannels or holes). FIG. 8 shows that robust heat transfer coefficientvalues (1000 to 3000 Watts/m²° K) are obtained within a practical rangeof 30% to about 90%.

FIGS. 9A, 9B and 9C depict the wafer as it is first placed on the chuck14 (of FIG. 2) prior to application of any chucking voltage (FIG. 9A),when the wafer is chucked to the puck with a minimal force (FIG. 9B),and when a very high chucking force is applied to realize a high heattransfer coefficient (FIG. 9C). Initially, the wafer has an equilibriumshape that includes a diameter-long bow (creating an initialpuck-to-wafer air or vacuum gap) and many small ripples (FIG. 9A). Inorder to couple across the relatively large air gap of FIG. 9A, a verylarge chucking D.C. voltage must be applied to pull the wafer down tothe puck, which removes the bow shape. This reduces the air gap, so thatthe wafer may now be held onto the chuck as in FIG. 9B with a much lowerchucking voltage, since the effective gap is now miniscule (on the orderof 5-10 microns or less). In FIG. 9B, the large bow in the wafer iseliminated, but the many ripples in the wafer shape persist. In order toensure a large heat transfer coefficient sufficient to maintain wafertemperature at high RF bias power levels (e.g., 5-10 kWatts), a largechucking voltage must be applied, in the range of 1-4 kVolts. The largeincrease in chucking voltage deforms the wafer shape so that the ripplesare at least partially flattened, but still can persist to a limiteddegree, as depicted in FIG. 9C. The greater chucking or contact force inFIG. 9C decreases the effective gap to as little as 1 micron or less,realizing a concomitant increase in wafer-puck heat transfercoefficient. FIG. 10 illustrates the chucking voltage as a function oftime, corresponding to the sequence of FIGS. 9A through 9C. In FIG. 10,the high contact force chucking voltage is depicted as being less thanthe initial chucking voltage required to overcome the air gap when thewafer is first placed on the chuck. However, the high contact forcechucking voltage may, instead, exceed the initial chucking voltage, asindicated in dashed line in FIG. 10. The application of an initiallyhigher chucking voltage than the later applied chucking voltage may alsoimprove the transient chucking force of the electrostatic chuck bydriving the mobile charge more quickly to near the surface of theelectrostatic chuck than otherwise possible with lower chucking voltage.

For higher wafer temperatures, the ESC may include one or more resistiveheaters, either embedded within the ESC or as a separate heaterthermally coupled to the ESC. The heated ESC may still include coolingchannels for a thermally conductive fluid. Alternatively, the ESC orheater may be thermally coupled to a heat sink. Heater power and/orcooling may be controlled by a temperature feedback control system. Forexample, a ceramic aluminum nitride (AlN) electrostatic chuck (ESC) 14includes the isolated electrode 62 embedded below the top surface(approximately 0.5-3 mm), and an isolated heater 75 a embedded severalmm below the isolated electrode. The ESC electrode connection and heaterconnections may be brought out separately through the backside of theESC. The heat sink 74 may be thermally coupled to the ESC backside. Asalternatives to the arrangement illustrated in FIG. 1, the heat sink 74may be bonded to the ESC 14, or alternatively, the heat sink 74 may bethermally coupled to the ESC 14 via a vacuum interface across a smallgap (i.e. 1 to hundreds of microns). The gas pressure in the gap may bevaried to control the thermal coupling between the ESC and heat sink, orthe gap may be varied. Alternatively, heat transfer fluid flow to theheat sink 74 may be switched on/off or varied continuously to controlthe thermal coupling between the ESC 14 and the heat sink 74. Such asystem may allow operating with high, controlled wafer temperature, evenas plasma source power and bias power are switched on/off or are varied.

For example, a wafer is to be plasma immersion ion implanted with boron,phosphorous or arsenic, using a hydride or fluoride dopant gas at awafer temperature of 100-1000 degrees C. (preferably degrees 600 C),using 50 W-2 KW (preferably 500 W) plasma source power in each of twotoroidal source conduits 22 a, 22 b (FIG. 11A) at an RF voltage of 0.3kV-10 kVpp (preferably 5 kVpp) and a pressure of 5-100 mtorr (preferably20 mtorr). The high wafer temperature may be desired, for example, to(1) maintain crystallinity of the implanted layer, (2) enhance theconcentration depth profile of implanted species, (3) enhance thediffusion of implanted species, (4) reduce the clustering of implantedspecies, or (5) improve the subsequent activation (by later annealprocess) of the implanted layer. The surface to be implanted may be asingle-crystalline bulk wafer or a SOI (silicon-on-insulator) layer.Alternatively, the surface to be implanted may be an amorphized layer ofa bulk wafer or SOI wafer, or may be an amorphous or polycrystallinedeposited layer over the bulk wafer or over an insulating layer.

The bias power required may be on the order of 10 W-10 KW, the majorityof which appears as heat load on the wafer. Initially the ESC cooling isset to a minimal level and the heater power is controlled to maintainthe ESC surface at a temperature greater than the target wafertemperature (670 C, with a variation of ˜50-100 C). The wafer isintroduced on the ESC 14, process gas is introduced and chamber pressureis regulated. Plasma source power and bias power are switched on orramped on and an ESC voltage is set to control the wafer temperature tothe desired 600 degree C. temperature with the added heat load of theplasma source and bias power, while approximately simultaneously thecooling of the heater/ESC is set to a high level to prevent overheatingof the ESC/heater. The heater power is varied by the closed loopESC/heater control system to maintain the heater/ESC at approximatelythe 660 degree C. setpoint. After the implant process is complete(typically 3 to 60 seconds, depending on target dose and RF voltage),the plasma is extinguished and the cooling of the heater or ESC is setto a low level and the heater power is varied by the closed loopESC/heater control system to maintain the heater/ESC at approximatelythe 660 degree C. setpoint.

Such a system may also be used for materials modification processes,surface cleaning processes, deposition processes, or etch processes.

Alternatively or in addition, the wafer to be implanted at hightemperature may be pre-heated to high temperature just prior to beingtransferred to the plasma immersion implantation chamber (in a pre-heatchamber) or may be pre-heated within the plasma immersion implantationchamber prior to implantation, for example by plasma heating. In thatcase, a non-reactive gas plasma operating with low or no wafer bias(source power only) is used to preheat the wafer, with the wafer 40thermally isolated from the ESC 14. For thermal isolation, the wafer 40may be positioned on the ESC 14 without electrostatically clamping it,or the wafer 40 may be positioned on lift pins above the surface of theESC. After pre-heating the wafer 40, the implantation process isinitiated. If the ESC 14 does not include a heater, the process iscarried out with the wafer 40 on the ESC 14, but thermally isolated (noelectrostatic clamping force) by appropriate ESC voltage selection. Ifthe ESC 14 does include the heater 75 (with adequate temperature controlcapability), the implant process is carried out as described earlier.

Multi-Mode Plasma and Neutral Processing Toroidal Source Reactor:

FIGS. 11A and 11B are cut-away side and top views, respectively of atoroidal source plasma reactor similar to that illustrated in FIGS. 1and 2, except that, in FIGS. 11A and 11B, the ceiling showerhead 18 isfed either by radicals from a remote plasma source (RPS) reactor 334 ordirectly from a process gas supply 313, depending upon the user'schoice. Preferably, the wafer support pedestal is a high contact forcewafer-cooling electrostatic chuck (ESC) of the type described above withreference to FIG. 1. The main elements of the reactor of FIG. 11Aincluding the wafer support or electrostatic chuck (ESC) 14 are the sameas described above with respect to FIG. 1, the same reference numeralsbeing employed in both drawings so that their description need not berepeated here. The toroidal source of FIG. 11A has a pair of transverseexternal reentrant conduits 22 a, 22 b with respective RF source powerapplicators 24 a, 24 b that include respective toroidal magnetic cores26 a, 26 b, respective conductive coils 28 a, 28 b wound around themagnetic core 26 a, driven by respective RF generators 30 a, 30 bthrough respective impedance match element 32 a, 32 b. The ceilingshowerhead 18 is surrounded by the toroidal reentrant transverse pathsof the oscillating plasma currents excited within the reentrant externalconduits 22 a, 22 b. The reentrant toroidal paths of the oscillatingplasma currents pass through the respective reentrant conduits 22 a, 22b and through the process region 42 overlying the surface of a wafer 40.

The process gas supply 313 contains different gas species, each of whichcan be accessed separately. A showerhead gas panel 336 a controls theselection and flow rate of gas species from the gas supply 313 to theshowerhead 18. The showerhead 18 can have a supply plenum 332 a and anoutput plenum 332 b separated by an apertured barrier 332 c. The bottomof the output plenum 332 b consists of a wall 332 d with gas injectionholes 332 e. A gas conduit 338 a receives the process gas and deliversit to the supply plenum 332 a. A main chamber gas panel 336 b controlsthe selection and flow rate of gas species from the gas supply 313 tothe gas injectors 20 of the main chamber 42 through a gas conduit 338 b.An RPS gas panel 336 c controls the selection and flow rate of gasspecies from the gas supply 313 to the RPS reactor 334. A gas conduit338 c conducts plasma products (e.g., excited and/or dissociatedneutrals or radicals) from an output port of the RPS chamber 334 to theshowerhead-supplying gas conduit 338 a. The drawings of FIGS. 11A and11B show a feed conduit 338 a feeding the ceiling showerhead 18 at itscenter with either radicals from the RPS chamber 334 or process gas fromthe gas panel 336 a. Uniform distribution of excited gas or radicalsinjected from the showerhead 18 into the main chamber 42 is attainedbecause the radicals from the conduit 338 a fill the supply plenum 332 aand pass through the apertured barrier 332 c to fill the output plenum332 b. Radical distribution in both plenums 332 a, 332 b is renderedmore radially uniform because gas or particle diffusion within theplenums 332 a, 332 b tends to overcome any distributionnon-uniformities. Therefore, the radial distribution of radicals (orprocess gases) across the array of injection holes 332 e is highlyuniform and is therefore uniform in the main chamber 42.

While the foregoing description pertains to a mode in which processgases are supplied directly to the supply plenum 332 a of the mainchamber showerhead 18 unless they are to be first excited or dissociatedin the RPS chamber 334, in other modes some (or all) of the processgases may be brought into the plenum 332 a behind the showerhead 18through the remote plasma source 334, even if some (or all) of theprocess gases are never used with the remote plasma source 334 turnedon. For example, one embodiment brings the following gases into theplenum 332 a via the RPS 334: O2, N2, H2, He, Ar, NF3. In this way thegas may be excited/dissociated by the RPS source 334, if desired, andoperated with or without plasma in the main plasma process chamberbelow. In a working embodiment, other (depositing) process gases aredelivered directly into the plenum 332 a, bypassing the RPS 334, butthis is not a requirement. Depositing or etching gases may be deliveredto the plenum 332 a through the RPS 334. There may be an advantage tobeing able to season the interior of the RPS chamber 334 by bringingdepositing gases through it. Of course, etching gases can be broughtthrough the RPS chamber 334 for cleaning the RPS itself, as well as forcleaning the main chamber 42.

The RPS reactor 334 can be any suitable type of conventional plasmareactor, such as a capacitively coupled reactor, an inductively coupledreactor or a toroidal source reactor, and may be a commerciallyavailable reactor of the type sold for use as a downstream externalplasma source. If it has a toroidal plasma source (e.g., of the typeemployed in the reactor of FIG. 1), then the RPS reactor 334 has anexternal reentrant conduit 334 a, a power applicator 334 b, an impedancematch 334 c and an RF power generator 334 d. It may have a bias powergenerator 334 e coupled through an impedance match 334 f to a biaselectrode 334 g in the RPS reactor 334.

The temperature of the chamber walls including the side wall 10 iscontrolling independently of the wafer temperature by a heatexchanger/pump 335-1 that pumps heat exchanging fluid through internalfluid passages 335-2 within the side wall 10 (and other chamber walls).In this way the chamber side wall 10 can be set to one temperature andthe wafer can be held at another temperature determined by the wafercontact force or applied chucking voltage. As will be discussed below,the chamber walls can be held at a temperature ideal for depositing ahigh quality (non-flaking) seasoning film (e.g., 20-60 degrees C.) whilethe wafer temperature can be held at a temperature that is too high forunwanted deposition to take place (i.e., above the deposition thresholdtemperature for the deposition of carbon polymers on a silicon surface)and that is too low for unwanted etching to take place (i.e., below theetch threshold temperature for a silicon wafer in a fluorine-containingplasma). An advantage is that no time is wasted or consumed whilewaiting for the temperature of the wafer support or ESC 14 to changebefore beginning wafer processing. Another advantage is that the wafertemperature can satisfy a processing requirement (e.g., prevention ofunwanted deposition during processing and prevention of unwanted etchingduring processing) while the side wall 10 and ESC 14 can be held atconstant temperatures that satisfy both a pre-processing need fordeposition of a high quality seasoning film and a post-processing needfor rapid removal of the seasoning film. These features are discussedlater in this specification.

Multiple Operating Modes of the Reactor:

The gas panels 336 a, 336 b, 336 c can be independently operated tofurnish different processes gases simultaneously to the showerhead 18(directly), to the main chamber gas injectors 20 (directly) and to theRPS reactor 334 so as to furnish neutral species or radicals from theRPS reactor 334 to the showerhead 18. Thus, there are three fundamentaloperational modes of the reactor as follows which may be carried outsingly at separate times or simultaneously, and are as follows: (a) afirst process gas (or gas mixture) is delivered to the main chamber gasinjectors 20, (b) a second process gas is delivered the showerhead 18,(c) a third process gas is delivered to the RPS reactor 334 which inturn generates radicals or dissociated neutrals that are delivered tothe showerhead 18 in lieu of (or in addition to) a process gas from thesupply 313. A number of additional modes are carried out by simultaneouscombinations of selected ones of the three basic modes (a), (b), (c),above. The multi-mode reactor of FIG. 11A therefore has a number ofpossible operational modes, some of which will be described below.

Advantages of the Multimode Toroidal Plasma Source Reactor:

One advantage of the coupling of the radical or dissociated neutralstream from the RPS reactor 334 to the main chamber showerhead 18 isthat the radial distribution of excited or dissociated neutrals in themain chamber 42 is so highly uniform that the excited or dissociatedneutrals may be used not only for chamber cleaning but also for waferprocessing. A related advantage is that the uniform radial distributionof excited or dissociated neutrals from the showerhead 18 renderschamber cleaning processes employing excited or dissociated neutralshighly uniform. This reduces consumption of chamber interior materialsduring cleaning processes and permits the chamber cleaning process to beaccomplished more quickly.

Processing wafers in a reactor having a toroidal plasma source with aexcited or dissociated neutral species (injected with uniform radialdistribution through the showerhead 18) solves the problem of performingrapid wafer cleaning in the toroidal source reactor without roughing orcompromising the quality of the wafer surface. In addition, plasma-basedwafer processes (such as plasma immersion ion implantation) may becarried out in the same chamber before or after wafer cleaning withexcited or dissociated neutral species, eliminating any necessity ofremoving the wafer from the chamber to perform both processes. Examplesdiscussed below in this specification include pre-implant wafer oxideremoval, post-implant photoresist strip or deposition removal, andmaterials enhancement using radicals. An advantage of performingpre-implant wafer oxide removal in the multi-mode chamber of FIG. 11A isthat the implant process can be performed immediately after oxideremoval and before the native oxide can return. (In conventionalprocesses, pre-implant wafer oxide removal is an acid dip step, and thenative oxide returns to some extent during wafer transport from the aciddip to the implant reactor.)

Another advantage is the rapid deposition and removal of an interiorchamber seasoning film before and after wafer processing. Referring toFIG. 12, a thin seasoning film 340 (e.g., several hundred angstroms toseveral microns in thickness) may be deposited on the chamber walls orsidewall 10 (and other interior surfaces, such as the workpiece supportor electrostatic chuck 14) so that all interior chamber surfaces arecoated with the film 340. This film consists of a process-compatiblematerial, and prevents the process-incompatible materials constitutingthe chamber interior elements and walls (such as aluminum, aluminumoxide aluminum nitride, stainless steel) from entering or contaminatingthe process. It also prevents consumption of those elements duringplasma processing. As disclosed in both above-referenced parentapplications, a thin process-compatible seasoning film may be depositedon the chamber interior surfaces prior to introduction of the wafer, inorder to prevent process contamination from metallic particles.Preferably, the seasoning film contains a significant amount of thereactive species of the process gas, to render the seasoning layerless-reactive or non-reactive with the process gas during waferprocessing. For example, for processes involving nitrogen-containingprocess gases, a silicon nitride film may be employed. For processesinvolving oxygen-containing process gases, a silicon dioxide film may beemployed. For processes involving a fluorinated or hydrated dopant gas,the seasoning film may be a fluorocarbon polymer or a hydrocarbonpolymer (respectively). Avoiding a combination of fluoride and hydrideradicals or ions in the chamber prevents excessive etching of either thewafer during wafer processing or of the chamber interior during chambercleaning processes.

A new seasoning film may be deposited on the chamber interior surfacesand then a batch of wafers may be processed in succession within thatchamber before the seasoning film is removed and replaced with a newseasoning film. However, it is felt that the best protection fromcontamination is realized by applying a new seasoning film each time awafer is to be introduced into the chamber, and then removing theseasoning film after processing of that wafer. To avoid significantproductivity loss from this procedure, the seasoning film deposition andremoval steps must be performed in less time than the time required toperform the wafer process (or less than a fraction of the wafer processtime). Rapid deposition of a high quality seasoning layer prior to waferprocessing is best accomplished in a deposition precursor gas using thetoroidal plasma source of the reactor of FIG. 11A. Rapid removal of theseasoning film 340 after wafer processing without excessive consumptionof interior chamber materials is accomplished by cleaning the chamberwith radicals injected through the showerhead 18 from the RPS reactor334. Such measures have reduced the pre-processing seasoning depositionand the post-processing seasoning removal to about 15 seconds.

Another process that is efficiently carried out in the multi-modereactor, but which can be performed in any reactor, eliminates orreduces backside wafer contamination that is occasioned by mechanicalinteraction or contact between the wafer backside and the surface of thewafer support pedestal or electrostatic chuck (ESC) 14. The process forreducing or eliminating wafer backside contamination consists ofdepositing an elastic film 342 (FIG. 12) on top of the wafer pedestal orESC surface before the wafer is introduced. For best results, thisprocess should be carried out with a high contact force wafer-coolingESC of the type described above with reference to FIG. 1, in which thetop surface is smooth and uninterrupted by open gas channels. In aconventional ESC, such open gas channels are required to accommodate athermal conductance-enhancing gas (e.g., helium). The ESC of FIG. 1 isgasless (i.e., uses no thermal conductance-enhancing gas, such asHelium, between the wafer and the chuck), and high thermal conductanceis achieved by high wafer contact force to the ESC (as described abovewith reference to FIG. 1). The combination of the flat uninterrupted ESCsurface and the elastic film reduces or eliminates wafer backsidecontamination. The elastic film is preferably a process compatiblematerial, such as a carbon-based polymer. For example, in processesemploying either a fluorinated or hydrated process gas, the elasticcushion layer can be a fluorocarbon polymer or a hydrocarbon polymer,respectively.

Deposition of the elastic film 342 on the ESC surface may be preceded byinitially depositing a hard protection layer, such as an oxide ornitride film, and thereafter depositing the elastic cushion layer orfilm 342. In this way, the ESC wafer support surface has an underlyinghard protection layer (not shown) covered by the elastic film 342.

For optimum results, the cushion film should be removed from the ESCafter each wafer is processed and a new cushion film should be depositedbefore processing of the next wafer. This requires rapid film depositionand removal to avoid a significant impediment to productivity. The mostrapid deposition process for a polymer cushion film on the ESC is aplasma enhanced CVD process, and the most rapid removal process withminimum consumption of chamber interior materials is a cleaning processusing radicals or dissociated neutrals (e.g., one or more of oxygen,nitrogen, hydrogen, fluorine) from the RPS reactor 334.

The problems of plasma immersion ion implantation etching the surfacebeing implanted and/or depositing an implant-inhibiting film formed fromthe ion implant process gas are solved by maintaining the wafertemperature during implantation within a temperature range at which bothetching of the surface being implanted and deposition of a film areinhibited or prohibited. Specifically, the wafer temperature range isabove the threshold temperature for deposition of the material formedfrom the process gas (e.g., a polymer-like boron hydride material, forexample) and below the threshold temperature for etching the surface(typically, crystalline, polycrystalline or amorphous silicon). Thewafer may be maintained within this optimal temperature range regardlessof plasma heat load using the gasless ESC that establishes high thermalconductivity by maintaining a large electrostatic contact force betweenthe wafer and the ESC. The etch and deposition behavior at the wafersurface is determined by both the wafer temperature and the plasma biasvoltage on the wafer, as well as the plasma conditions (gas chemistry,flow rates, process pressure, source power). Specifically, the thresholdetch temperature and the threshold deposition temperature are differentfor different wafer bias voltage levels. If the wafer process to beperformed is a plasma immersion ion implantation process, then the biasvoltage must be set to attain the required ion implantation depth ordepth profile. This fixes the etch and deposition threshold temperaturesfor a given process chemistry and set of process conditions (e.g.,chamber pressure). Thereafter, the wafer temperature is set (by settingthe ESC wafer clamping force) to a value lying above the thresholddeposition temperature and below the threshold etch temperature. We havefound that this temperature range depends upon the process gaschemistry. For example, the greater tendency of fluoride dopant gases toetch decreases the requisite temperature range. The greater tendency ofhydride dopant gases to deposit a film in the wafer increases therequisite temperature range. As a result, the ideal “no etch/nodeposition” wafer temperature range is generally lower for fluoridedopant gases and is generally higher for hydride dopant gases. This willbe seen in some of the working examples given below in thisspecification.

The “no etch/no deposition” wafer temperature range may further bemodified by adding another dilution gas. For example, for a dopanthydride implantation process, hydrogen may be added (as a dilution gas)to reduce deposition at a given wafer temperature and implantationvoltage. Conversely, hydrogen may be added to allow lower wafertemperature without deposition. If sufficient hydrogen is added to thedopant hydride implantation process, etching of the implanted surfacemay result. If this is excessive, the wafer temperature may be reducedto suppress etching.

Hydrogen may alternatively or additionally be added to suppressoxidation of the wafer surface which can occur during implantation.Oxidation of the implanted surface, of a dopant-rich layer in theimplanted surface or of a thin deposited dopant-containing layer, maytrap dopant species at or near the surface, limiting subsequent dopantdiffusion and/or activation. Hydrogen may be added to (1) reduceoxidation, (2) enhance the concentration depth profile of implantedspecies, (3) enhance the diffusion of implanted species, (4) reduce theclustering of implanted species, or (5) improve the subsequentactivation (by later anneal process) of the implanted layer. Thehydrogen dilution gas may be H2 or another suitable hydrogen-containinggas.

Hydrogen may be added as the diluent gas in dopant-fluoride implantationprocesses. While this addition may not improve etching loss of theimplanted surface, hydrogen may be added to (1) reduce oxidation, (2)enhance the concentration depth profile of implanted species, (3)enhance the diffusion of implanted species, (4) reduce the clustering ofimplanted species, or (5) improve the subsequent activation (by lateranneal process) of the implanted layer.

Co-implantation (simultaneous or sequential) of dopant species (such asa dopant hydride or a dopant fluoride, e.g., B2H6 or BF3) with adeposition species, such as SiH4, GeH4, SiF4 or GeF4 may be useful in(1) compensating etch loss, (2) enhancing the concentration depthprofile of implanted species, (3) enhancing the diffusion of implantedspecies, (4) reducing the clustering of implanted species, or (5)improving the subsequent activation (by later anneal process) of theimplanted layer.

Processes Performed in the Multi-Mode Reactor:

Referring to FIG. 13, the multi-mode reactor of FIG. 11A can efficientlycarry out a complete ion implantation process in which the chamberinterior is quickly seasoned, the wafer is cleaned by radicals injectedthrough the showerhead, plasma immersion ion implantation is performed,and the chamber seasoning is removed by radicals injected through theshowerhead. While the foregoing contemplates the cleaning processes(i.e., the process for cleaning or deoxidizing the wafer and the processfor cleaning or removing the seasoning layer from the chamber interiorsurfaces) are carried out by introducing radicals or excited neutralsfrom the RPS chamber 334, either or both such cleaning processes couldbe carried out without the RPS chamber by introducing cleaning precursorspecies in to the main chamber 42 and striking a plasma in the mainchamber 42. Alternatively, either or both such cleaning process could becarried out by a combination of both excited neutrals from the RPSchamber 334 introduced into the main chamber 42 and a plasma of cleaningspecies in the main chamber 42.

In the step of block 350 of FIG. 13, the chamber interior surfaces suchas the side wall 10 are held at a temperature sufficiently low (e.g.,60-75 degrees C.) to promote chemical vapor deposition of a high quality(non-flaking) seasoning film consisting of a process-compatible materialsuch as a fluorocarbon polymer or a hydrocarbon polymer. This caninclude the ESC top surface, which is also held at a low temperaturesuitable for deposition. The wafer temperature can be different (e.g.,about room temperature to over 1000 degrees C., if a heater/ESC is used)during the subsequent wafer processing, depending upon the electrostaticor clamping force applied by the ESC 14 to the wafer and the wafer heatload and thus plasma source and bias power, without having to change thetemperature of the ESC. The advantage is that no time is wasted orconsumed while waiting for the ESC temperature to change beforebeginning wafer processing. Another advantage is that the wafertemperature can satisfy a processing requirement (e.g., prevention ofunwanted deposition during processing and prevention of unwanted etchingduring processing) while the wall and ESC temperature can be held at aconstant temperature that satisfies both a pre-processing need fordeposition of a high quality seasoning film and a post-processing needfor rapid removal of the seasoning film.

In the next step of FIG. 13 (block 352), a seasoning film precursor gasis introduced into the main chamber 42, either through the ceilingshowerhead 305 or through the side gas injection nozzles 20. Theprecursor gas can be a fluorocarbon or hydrocarbon gas for a polymerseasoning film, a combination hydrocarbon/fluorocarbon gas for combinedhydrofluorocarbon film, a polymer enhanced with Si, Ge, B, P, or Asusing hydrides or fluorides of said materials, a mixture of nitrogen andsilane for a silicon nitride film, silane and oxygen for a silicondioxide film, silane or silane plus hydrogen for a silicon or siliconhydride film, or other suitable gases or gas mixtures. If the ionimplantation is to be performed with a fluorinated or hydrated dopantgas, then the preferred seasoning film is a fluorocarbon or hydrocarbon,respectively. Next, a plasma-enhanced chemical vapor deposition step isperformed (block 354) by applying plasma source power to the externalconduits 22 a, 22 b of the main chamber. The seasoning precursor gas isremoved (block 356) and a wafer is placed on the ESC 14 (block 357). Apre-implant wafer clean process is performed by introducing an oxideremoval species precursor gas (such as hydrogen) into the RPS chamber334 (block 358 of FIG. 13) and applying plasma source power to the RPSchamber 334 to generate radicals that are fed through the showerhead 305into the main chamber, and perform a radical-based cleaning or oxideremoval process on the wafer 40 (block 359 of FIG. 13). Theradical-based cleaning removes the wafer oxide in a relatively gentlemanner that avoids damaging or degrading the smooth surface of thewafer. The wafer is maintained at the desired process temperature—e.g.,below the etch threshold temperature and above the deposition thresholdtemperature—(block 360) and an ion implant species precursor gas isintroduced (block 361) into the main chamber 42. Source power is applied(block 362) and bias power is applied (block 364), the bias power beingsufficient to impart an ion energy corresponding to the desired implantdepth and carry out the plasma immersion ion implantation step.

The wafer is removed from the chamber (block 366) and a seasoning filmremoval species precursor gas (e.g., oxygen-containing gas such as O2for removing a fluoro- or hydro-carbon polymer seasoning film (possiblyin combination with one or more of hydrogen, fluorine or nitrogencontaining gas such as H2, NF3, N2, NH3), or NF3 or NH3 for removingother materials) is introduced into the RPS chamber 334 (block 368). Theradicals produced in the RPS chamber 334 are drawn into the main chamber42 to carry out a seasoning removal step which cleans all of the chamberinterior surfaces (block 370). In order to maintain an adequate flow ofradicals from the RPS chamber 334 to the main chamber 42, the mainchamber 42 may be maintained at a lower pressure than the RPS chamber334. The radicals or dissociated neutrals efficiently remove theseasoning film from the internal chamber surfaces in a manner that isrelatively gentle and avoids excessive consumption of chamber interiormaterials. Alternatively or additionally, plasma source power may beapplied to generate a cleaning plasma within the chamber.

The seasoning film may be deposited on the chamber interior surfaces ofthe multi-mode reactor of FIG. 11A prior to wafer processing and removedafter wafer processing in connection with any suitable type of waferprocess. This general concept is illustrated in FIG. 14. First, theseasoning layer is deposited on the chamber interior surfaces, which isthe block in FIG. 14 labeled 350, 352, 354 corresponding to theidentical steps of FIG. 13. The wafer is introduced (block 357 of FIG.14) and a wafer process is performed in the chamber (block 371 of FIG.14). Thereafter, the wafer is removed (block 366 of FIG. 14) andradicals (from the RPS chamber 334) are introduced through theshowerhead 18 to remove the seasoning film from the chamber interiorsurfaces (block 368 of FIG. 14). The multi-mode reactor is particularlyuseful in cases where the wafer process of block 371 requires radicalsto carry out. In such a case, the multi-mode reactor of FIG. 11Aprovides highly uniform distribution of radicals across the wafersurface because the showerhead 18 injects the radicals in a highlyuniform manner. FIG. 15 illustrates such a process.

Referring to FIG. 15, a seasoning film is deposited on the chamberinterior surfaces in the steps are blocks 350, 352, 354 and 356, whichhave been described above with reference to FIG. 13. The next step is tointroduce a wafer (block 357) and a processing precursor gas into theRPS chamber 334 (block 359) and apply plasma source power to the RPSchamber 334 (block 362 of FIG. 15). The dissociated neutrals flow fromthe RPS chamber 334 through the showerhead 18 and into the main chamber42 to support a wafer processing step (block 365). The wafer process ofblock 365 may be any suitable process that employs radicals ordissociated neutrals. For example, the process may be any one of thefollowing: a pre-implant wafer oxide removal process (block 365-1), aphotoresist strip process (block 365-2), a wafer cleaning processcarried out immediately before deposition of an epitaxial layer (block365-3), gate oxide nitridation in a radical mode (block 365-4), ormaterials enhancement (block 365-5).

The pre-implant wafer oxide removal process of block 365-1 may becarried out with hydrogen radicals. The photoresist strip process ofblock 365-2 may be carried out with oxygen radicals. The pre-depositionwafer clean process of block 365-3 may be carried out with fluorine,hydrogen, ammonia or oxygen (or possibly oxygen+nitrogen) radicals,depending upon the film composition then present on the wafer. The gateoxide nitridation step of block 365-4 may be carried out with nitrogenradicals for a silicon dioxide gate insulator layer, using for example,N2 or NH3. The materials enhancement process of block 365-5 may becarried out with fluorine radicals for treating a tantalum or titaniumgate electrode, using for example, F2, NF3, SiF4, or a fluorocarbon gas.As a further application, plasma or radical oxidation may be used foroxide growth, such as for gate oxide grown at low temperature (ascompared with pure thermal gate oxide growth process). One example ofsuch an application uses O2 and/or water vapor to grow plasma oxide at awafer temperature of 600 degrees C., using O2 plasma generated in themain chamber 42 or O2 radicals from the RPS 334.

Upon completion of the wafer process of block 365, the wafer is removedfrom the reactor (block 366 of FIG. 14) and the chamber seasoning filmis removed in the steps of blocks 368 and 370 using radicals from theRPS chamber 334, as described above with reference to FIG. 13.

The multi-mode reactor of FIG. 11A may be operated in more than one itsbasic modes simultaneously. FIGS. 16 and 17 illustrate processes thatuse both the RPS reactor source power and the main chamber source powersimultaneously. In the process of FIG. 16, a non-reactive species gas isintroduced into the RPS reactor 334 while a reactive species gas isintroduced into the main chamber 42 through the side nozzles 20. Sourcepower is applied to both chambers 42, 334. The excited non-reactive gasspecies generated in the RPS chamber 334 enter the main chamber 42through the showerhead 18. Some of the excited non-reactive gas atoms ormolecules collide inelastically with the reactive species and maydissociate the reactive species. This assists the main chamber sourcepower in generating a plasma and may possibly reduce the amount ofsource power required in the main chamber. In FIG. 16, the first step isto season the reactor chamber interior (block 380). A wafer is placed onthe ESC 14 (block 381). A non-reactive gas is introduced into the RPSchamber 334 and source power is applied in the RPS chamber to excite thenon-reactive gas (block 382) to produce excited non-reactive gas speciesthat enter the main chamber through the showerhead 18 (block 383).Simultaneously, a reactive species precursor gas is introduced into themain chamber (block 384) which is dissociated by collisions with theexcited non-reactive gas species that entered through the showerhead 18.If the energy of the excited non-reactive gas species is sufficient, itmay be unnecessary to apply any plasma source power in the main chamber42. However, a modest amount of source power applied to the main chamber42 produces a plasma with the desired ion density. This step carries outa plasma-enhanced wafer processing step. Upon completion, the wafer isremoved (block 385) and the seasoning layer is removed from the chamber(block 386) preferably in the manner described above using radicals fromthe RPS reactor 334.

In the process of FIG. 17, a reactive gas is dissociated in the RPSchamber to provide dissociated reactive species or radicals through theshowerhead 18 into the main chamber. Referring now to FIG. 17, theprocess of FIG. 17 can include initially coating the chamber interiorwith a seasoning film (block 380) before the wafer is introduced (block381) as in the process of FIG. 16. A reactive gas is dissociated in theRPS chamber 334 (block 387) to provide dissociated reactive species orradicals through the showerhead 18 into the main chamber 42 (block 388).Simultaneously, plasma source power is applied in the main chamber toionize a portion of the radicals in the main chamber (block 389). Thewafer is therefore exposed to both radicals and ions in a desiredproportion. This process is particularly useful for a process in which alayer is to be doped with a material-enhancing species to a precisedepth. The use of radicals in this process provides good depth control,while the use of ions in the process can enhance productivity where therequired depth is relatively great. One example is the enhancement of athick gate oxide layer (such as hafnium oxide) with fluorine atoms tomodify the gate oxide dielectric constant. In such a process, the depthprofile of the fluorine atoms is critical because the underlyingsemiconductor layer cannot tolerate contamination with fluorine. Anotherexample is the enhancement of a tantalum or titanium gate with fluorineatoms to modify the metal work function. The foregoing is followed byremoving the wafer upon completion of the wafer process (block 385) andthen removing the chamber seasoning film (block 386).

FIG. 18 illustrates a process that can be carried out in any plasmareactor for eliminating or reducing contamination. The process is bestcarried out, however, by first providing (block 390 of FIG. 18) apolished flat continuous wafer support surface on the reactor's wafersupport pedestal in the chamber. Preferably, the wafer support pedestalis an electrostatic chuck (ESC) having such a continuous polishedsurface, and may be of the type described in detail above with referenceto FIGS. 1-10 that is free of any open gas channels in its top surface.This type of ESC can be used with any type of plasma source to carry outthe process of FIG. 18 in a reactor chamber, including a toroidal plasmasource (as in FIG. 11A), an inductively coupled source, a capacitivelycoupled source or a microwave source or other source. A gas containingthe precursor of an elastic material is introduced into the reactorchamber (block 391 of FIG. 18). The elastic material may be afluorocarbon polymer, a hydrocarbon polymer or a fluoro-hydrocarbonpolymer, and the precursor gas is then a fluorocarbon gas, a hydrocarbongas or a fluoro-hydrocarbon gas or mixture, respectively. A plasma isgenerated from the process gas while the chamber pressure, gas flow rateand surface temperature of the ESC are set to promote chemical vapordeposition of the elastic material onto the wafer-supporting surface ofthe wafer support pedestal (block 392 of FIG. 18). The elastic materialforms a cushioning film on the ESC that will prevent harsh contact andscraping between the wafer backside and the top surface of the ESC.After the cushioning layer has reached a desired thickness (e.g.,several hundred angstroms to several microns), the process gas isremoved from the chamber (block 393) and the wafer is introduced intothe chamber and placed on the cushioning layer formed on the ESC (block394 of FIG. 18). If the wafer support pedestal is an ESC, then the waferis electrostatically clamped over the cushioning layer. A wafer processis then carried out (block 395 of FIG. 18) by introducing a suitableprocess gas into the chamber and coupling plasma source power into thechamber (or by introducing dissociated neutrals from an RPS chamber).Required process conditions are maintained in the chamber until thewafer process has been carried out (block 396). Then, the wafer isremoved (block 397), and the cushioning layer is removed from the wafersupport pedestal by introducing a cleaning species precursor process gasinto the chamber (block 398). Preferably, the cleaning species precursorprocess gas has been dissociated prior to its introduction into thereactor chamber, and very little or no plasma source power is requiredto remove the cushioning film from the wafer support pedestal.Alternatively, the cleaning species is generated within the processchamber by application of plasma source and/or bias power.

Three-Element Independent Temperature Control:

The high contact force ESC of FIGS. 1-10 controls the wafer temperatureseparately from the ESC temperature and independently of the chamberwall temperature, permitting these three elements to be held at threedifferent temperatures. This feature facilitates rapid deposition andremoval of the chamber seasoning film to meet the twin requirements ofhigh productivity and low metal contamination or particle count on thewafer, as will be explained below.

The wafer temperature is determined by a balance between theelectrostatic contact force-induced thermal conductivity to the ESC, theESC temperature and the plasma heat load. Thus, the ESC can be at onetemperature while the wafer can be at a higher temperature, dependingupon the electrostatic contact force. The greater the ESC-wafer contactforce, the closer the wafer temperature is to the cooler ESCtemperature. The only requirement for the ESC temperature is that it besufficiently cool to enable temperature control of the wafer. Thispermits the wafer temperature, the ESC temperature and the chamber walltemperature to be different from one another. These three differentelements (the wafer, the walls and the ESC) can meet differenttemperature requirements. The wafer is preferably held at a temperaturethat satisfies the requirements of a particular wafer process recipe.This can be as high as 600 degrees C. or higher to prevent amorphizationduring an ion implantation process, as one example. Or, if a hydride orfluoride dopant gas is employed for dopant implantation, the wafertemperature can be sufficiently low (e.g., about 5 degrees C.) to avoidetching of the wafer and sufficiently high to avoid deposition of apolymer-like film (e.g., BH3). The chamber walls are preferably held ata temperature at which a high quality chamber seasoning film can berapidly formed and later rapidly removed. This may be about 20-80degrees C. depending upon the seasoning film chemistry. The ESC 14 ispreferably held at a temperature that is sufficiently cool to meetplasma heat load on the wafer and which promotes rapid deposition of ahigh quality cushioning film on its wafer support surface and/or aseasoning film on all its surfaces, and removal of such films within areasonable time. An optimum ESC temperature therefore may be less thanthe temperature of the chamber walls, and is preferably in the range of−20 to +60 degrees C.

The seasoning film and/or cushioning film is preferably deposited andremoved very rapidly in order to permit its frequent replacement withoutexcessively reducing productivity (relative to conventional processes inwhich no seasoning film is periodically removed and replaced). For thisreason, it is preferred that the chamber seasoning deposition andremoval time be on the order of the wafer process time (or less). Forwafer process times on the order of a minute or minutes (such as aplasma immersion ion implantation step), this leaves very little timefor the pre-process seasoning deposition step and the post-processingseasoning removal step. This time is too short for the heat exchangers327 or 335-1 to change the temperature of the chamber walls or the ESCby any significant amount. Therefore, it is preferred to select arespective optimum temperature for each of the respective elements(i.e., the chamber walls, the ESC and the wafer), and hold theseelements at their respective temperatures throughout processing.Accordingly, prior to chamber seasoning, the chamber sidewall ispermanently set to its optimum temperature and the ESC is set to itsoptimum temperature. Upon introduction of the wafer, the ESC chuckingvoltage is set to a level that puts the wafer temperature at its optimumlevel, where it is held until the completion of wafer processing. Thewall temperature and ESC temperature continue unchanged during removalof the seasoning film, in a preferred embodiment.

The processes described above for rapid pre-process deposition of aseasoning layer and post-process removal of the seasoning layer may becarried out in similar fashion in the RPS chamber 334. In this way, theRPS chamber interior surfaces may be coated with a seasoning layer priorto wafer processing in the main chamber 42 and the seasoning layer inthe RPS chamber 334 may be removed upon completion of wafer processingin the main chamber 42.

Preferred Process Chemistries:

For plasma immersion ion implantation processes employing either afluoride-based dopant gas (e.g., BF3) or a hydride-based dopant gas(e.g., PH3), it is preferred to employ a fluorocarbon polymer orhydrocarbon polymer, respectively. Although a fluoro-hydrocarbon polymercan be employed, it is preferred to not combine fluorine and hydrogentogether in the same process, as their combination can promote etchingof the wafer (and of consumable materials in the chamber interior) to anexcessive degree. A fluorocarbon polymer is resistant or impervious toetching by a fluoride dopant gas, while a hydrocarbon polymer isresistant or impervious to etching by a hydride dopant gas. Such polymerfilms effectively prevent or nearly prevent metallic contamination ofthe wafer, even in the presence of very high energy ions such as may berequired for ion implantation. Using the procedures described in theprevious paragraph with a fluorocarbon seasoning layer and a BF3 dopantprocess gas at very high ion energy (6 KV to 8 KV bias voltage), we haveachieved extremely low particle and surface metallic contaminationcounts on the wafer front side and back side (less than 0.05 particlesof size greater than 0.1 um per square cm wafer area and less than 1E10metal atoms/cm2, respectively) with a seasoning deposition time lessthan the ion implantation time and a seasoning removal time less thanthe ion implantation time.

While fluoride dopant process gases have a greater tendency to etch thewafer, hydride dopant gases have a greater tendency to deposit a film onthe wafer. Such unwanted deposition can be reduced by increasing thewafer temperature. If such an increase in temperature is not desired,then the unwanted deposition can be reduced by introducing diluent gasesduring ion implantation, such as H2 or N2 or NH3 (which promotes etchingof the deposited material) and He or Ar or Ne or Xe (which promotes ionbombardment of the deposited film). Oxygen may also be added in verysmall amount to control deposition, but excessive oxygen may causeoxidation of the Si surface. Fluorine-containing gas may be added tocontrol deposition by introducing an etch component. Thefluorine-containing gas may be a complimentary dopant fluoride of thesame p-type or n-type dopant (ie. BF3 added to a B2H6 or B5H9 dopingprocess, or PF3 or AsF3 or AsF5 added to a PH3 or AsH3 doping process)or may be another fluoride such as SiF4, GeF4, NF3, HF or F2. Therelative amount of the fluoride is selected to be small enough tominimize Si loss of the surface being implanted.

While the foregoing describes the surface being implanted as beingcomprised of Si, it may alternatively be comprised of Ge or SiGe orother semiconductor material or other material.

The preferred gas chemistry for depositing the chamber seasoning filmprior to a plasma immersion ion implantation step employing a fluoridedopant gas is C4F6 or C3F6. Other fluorocarbon gases include C2F4, C2F6,C3F8, C4F8 and C5F8. As noted above, fluoro-hydrocarbon polymers may beemployed for the chamber seasoning layer, but it is preferred to avoidcombining fluorine and hydrogen in the process because such acombination promotes etching to an excessive degree. The fluoride dopantgas may be any one of BF3, AsF5, AsF3, PF3. In addition, thefluorocarbon seasoning film may be used for plasma immersion ionimplantation with a non-dopant fluoride process gas, such as F, SiF4,GeF4 and the like.

The preferred gas chemistry for depositing the chamber seasoning filmprior to a plasma immersion ion implantation step with a hydride dopantgas is C3H6 or C4H6. Methane (CH4) can work but is not preferred becauseits high hydrogen content tends to depress its deposition rate. Otherhydrocarbon process gases for this purpose include C2H2, C2H4, C2H6,C3H8, C4H8, C4H10, C5H12, C6H14. As noted above, fluoro-hydrocarbonpolymers may be employed for the chamber seasoning layer, but it ispreferred to avoid combining fluorine and hydrogen in the processbecause such a combination promotes etching to an excessive degree. Thehydride dopant gas may be B2H6, B5H9, B10H14, PH3, AsH3 and the like. Ahydrocarbon polymer is also useful as a chamber seasoning layer fornon-dopant implantation species such as nitrogen or hydrogen. However,it is preferred to not use it with ion implantation of oxygen, becauseoxygen is an etchant of a carbon polymer.

If it is desired to use a carbon polymer in connection with anoxygen-containing process gas or in connection with plasma immersion ionimplantation of oxygen, then the polymer seasoning layer can be hardenedto resist attack by oxygen (or other species) by doping or enriching itwith silicon or germanium. Thus, a fluorocarbon polymer precursor gasemployed during chamber seasoning film deposition should be augmentedwith a silicon- or germanium-containing gas such as SiF4 or GeF4, butalternatively could be augmented with SiH4 or GeH4 or metallorganic Sior Ge sources. Similarly, the hydrocarbon polymer precursor gas employedduring chamber seasoning film deposition should be augmented with asilicon- or germanium-containing gas such as SiH4 or GeH4, butalternatively could be augmented with SiF4 or GeF4 or metallorganic Sior Ge sources. Such a hardened polymer is not rapidly removed with anoxygen cleaning gas. Preferably, rapid removal of such a hardenedpolymer seasoning layer is accomplished by adding fluorine and/orhydrogen to the cleaning gas, which may therefore be a combination oftwo or more of oxygen, hydrogen and fluorine The cleaning process can befurther hastened by striking a plasma in the chamber and applying asignificant bias voltage to the wafer support pedestal to increase ionbombardment energy in the chamber. Cleaning using a plasma in thechamber does not require that the RPS source be used.

Seasoning may alternatively or additionally be performed using noncarbon-based materials. For example, the chamber and/or ESC may beseasoned with a plasma process that uses the dopant hydride or fluoridegas that will be used in the subsequent plasma immersion ionimplantation process. Alternatively the chamber and/or Esc may beseasoned with a combination of dopant and silicon-containing gas such asSiH4 or SiF4 or germanium-containing gas such as GeH4 or GeF4.Alternatively the chamber may be seasoned with compound of the dopantmaterial, such as a dopant oxide, nitride, carbide, by using, forexample, a plasma containing BF3 or B2H6 and O2, N2, or C3H6,respectively. Alternatively the chamber/ESC may be seasoned with asilicon, silicon-hydride, silicon-oxide, silicon-nitride, orsilicon-oxynitride film using for example SiH4, SiH4 and H2, SiH4 andO2, SiH4 and N2, or SiH4 and O2 and N2, respectively. Alternatively oradditionally, the chamber/ESC may be seasoned with a germanium,germanium-hydride, germanium-oxide, germanium-nitride, orgermanium-oxynitride film using for example GeH4, GeH4 and H2, GeH4 andO2, GeH4 and N2, or GeH4 and O2 and N2, respectively.

Working Examples:

Plasma immersion ion implantation using a fluoride dopant gas (such asBF3) with a bias voltage of 1 kV can be carried out using ESCtemperature in a range between −40 and +60 degrees C., the preferredrange being between 0 and +40 degrees C., a chamber wall temperature inthe range of 0 to 120 degrees C., the preferred range being 20 to 80degrees C. If the bias voltage is increased to 8 kV, then the maximumESC temperature decreases to 60 degrees C. and the preferred maximum ESCtemperature decreases to 20 degrees C. The foregoing assumes that Sietching loss be limited to much less than 10 Angstroms. For a hydridedopant gas, the temperature range tends to be higher, because, comparedto fluoride dopant gases, hydride dopant gases tend to etch less andpromote more deposition: at 1 kV bias and 500 watt source power, the ESCtemperature range is 0 to 80 degrees C., the preferred range being 20 to60 degrees C. At 8 kV, a lower temperature is better, the range beingdecreased to −20 to 60 degrees C. and the preferred range being 0 to 40degrees C. For implant processes involving either hydride or fluoridedopant gases at either a high (8 kV) or low (1 kV) bias, the chamberpressure range is 5 to 200 mT, the preferred range being 10 to 100 mT.For a high conformality implant profile, the pressure range is 50-200mT, the preferred pressure range being 60-100 mT. For a low conformalityimplant profile, the pressure range is 5 to 45 mT, the preferredpressure range being 10-30 mT. The source power range is 50 W to 3 kWper reentrant conduit, the preferred range being 100 W to 1 kW. The ESCwafer clamping D.C. voltage (which determines the wafer temperature) isin the range of 100 to 1000 V, the preferred range being 200 to 400 V.

In one example of a low energy plasma immersion ion implantation processfor implanting a crystalline Si wafer or preamorphized Si wafer withboron with a fluoride dopant gas, the RF bias voltage was 1 kV, thedopant gas was BF3 at a flow rate of 20 sccm, the ESC temperature was 5degrees C., the chamber wall temperature was 60 degrees C., the sourcepower was 500 watts for each reentrant conduit, the process chamberpressure was 15 mtorr, and the wafer clamping voltage on the ESC was 200volts D.C. In this example, the bias voltage may be increased to 8 kV totransform the process into a higher energy process without changing theother parameters. An implant time of 20 seconds and an RF bias voltageof 2.85 KV on a preamorphized (80 keV Ge, 5E14/cm2) Si wafer yielded asheet resistance of about 372 ohms/square, a retained dose of 4.5E15atoms/cm3, and an annealed junction depth of about 430 angstroms(defined by a boron concentration at the 5E18/cm3) following a spikeanneal at 1050 degrees C. The foregoing contrasts favorably with abeamline implant process implanting B+ at a dose of 3E15 atoms/cm2 at anenergy of 500 eV, decelerated from 2 keV, which had a sheet resistanceof 393 ohms/square and an annealed junction depth of about 425 angstromswith the same anneal.

As employed in the foregoing paragraph, the term preamorphization refersto a pre-ion implantation process of damaging a crystalline materialwith ion bombardment in order to reduce or prevent channeling during thesubsequent ion implantation process. Preamorphization produces anamorphous structure over some depth profile (that is a function of theimplanted specie mass, energy, dose and angle of incidence with respectto the surface, and of the material or mass and structure beingimplanted). It is often performed to improve the subsequent junctionformation process, as an amorphous structure reduces or eliminateschanneling of implanted ions, yielding a shallower junction with betterabruptness than a crystalline material. The shallower junction withequivalent resistance can provide better device switching performance.

If the low energy ion implantation process for implanting a crystallineSi wafer or preamorphized Si wafer with boron is used with a hydridedopant gas such as B2H6, then the ESC temperature is increased to 25degrees C. and the gas flow rate is decreased to 10 sccm. In addition adiluent gas flow of 90 sccm of He and 50 sccm of H2 is added. In thisexample, the bias voltage may be increased to 8 kV to transform theprocess into a high energy process without changing the otherparameters. An implant time of 10 seconds and an RF bias voltage of 2.85KV on a preamorphized Si wafer yielded a sheet resistance of about 353ohms/square, a retained dose of 7.7E15 atoms/cm3, and an annealedjunction depth of about 420 angstroms (defined by a boron concentrationat the 5E18/cm3) following a spike anneal at 1050 degrees C.

In another example of a low energy plasma immersion ion implantationprocess for implanting a crystalline Si wafer or preamorphized Si waferwith boron with a fluoride dopant gas, the RF bias voltage was 1 kV, thedopant gas was BF3 at a flow rate of 20 sccm, the ESC temperature was 5degrees C., the chamber wall temperature was 60 degrees C., the sourcepower was 100 watts for each reentrant conduit, the process chamberpressure was 40 mtorr, and the wafer clamping voltage on the ESC was 200volts D.C. In this example, the bias voltage may be increased to 8 kV totransform the process into a high energy process without changing theother parameters.

In another example of a low energy ion implantation process forimplanting a crystalline Si wafer or preamorphized Si wafer with boronwith a hydride dopant gas such as B2H6, then the ESC temperature isincreased to 25 degrees C. and the gas flow rate is decreased to 10sccm. In addition a diluent gas flow of 90 sccm of He and 50 sccm of H2is added. The source power was 100 watts for each reentrant conduit, theprocess chamber pressure was 40 mtorr, and the wafer clamping voltage onthe ESC was 200 volts D.C. In this example, the bias voltage may beincreased to 8 kV to transform the process into a high energy processwithout changing the other parameters.

In the two preceding examples, increasing the chamber pressure mayincrease the conformality of the implantation. Alternatively, theprocesses may be carried out with 0 watts source power with somereduction in dose rate, or at 70 mtorr with little or no reduction indose rate relative to the example at 100 watt and 40mtorr.

In one example of a low energy plasma immersion ion implantation processfor implanting a wafer with a surface comprised of deposited film of 700angstroms thickness of amorphous Si or polycrystalline Si over an oxideisolation layer of 40 angstrom thickness with boron with a fluoridedopant gas, the RF bias voltage was 2 kV, the dopant gas was BF3 at aflow rate of 20 sccm, the ESC temperature was 25 degrees C., the chamberwall temperature was 60 degrees C., the source power was 100 watts foreach reentrant conduit, the process chamber pressure was 40 mtorr, andthe wafer clamping voltage on the ESC was 200 volts D.C. Alternatively,the process may be carried out with 0 watts source power with somereduction in dose rate, or at 70 mtorr with little or no reduction indose rate relative to the example at 100 watt and 40 mtorr. An implanttime of 60 seconds yielded a Si layer sheet resistance of about 1200ohms/square following a 20 second anneal at 960 degrees C., comparedwith a beamline implant process implanting B+ at a dose of 5E15atoms/cm2 at an energy of 3 keV, which had a sheet resistance of 590ohms/square with the same anneal. The RF bias voltage and implant timemay be adjusted (up or down) to optimize the sheet resistance of theannealed Si layer thickness.

If the low energy ion implantation process for implanting a wafer with asurface comprised of deposited film of 700 angstroms thickness ofamorphous Si or polycrystalline Si over an oxide isolation layer of 40angstrom thickness with boron is used with a hydride dopant gas such asB2H6, then the ESC temperature is increased to 35 degrees C. and the gasflow rate is 10 sccm. In addition a diluent gas flow of 90 sccm of Heand 50 sccm of H2 is added. The other parameters are kept about the sameas the previous example. An implant time of 60 seconds yielded a Silayer sheet resistance of about 570 ohms/square following a 20 secondanneal at 960 degrees C. The RF bias voltage and implant time may beadjusted (up or down) to optimize the sheet resistance of the annealedSi layer thickness.

In the preceding examples, increasing chamber pressure may increase theconformality of the implantation.

When implanting an isolated semiconductor layer as in the preceding twoexamples (implanting a wafer with a surface comprised of deposited filmof amorphous Si or polycrystalline Si over an oxide isolation layer)where it is desired to dope the entire layer thickness to achieve atarget resistivity after anneal (in contrast to forming a semiconductorpn junction), a combination of deposition and implantation may beadvantageously combined to maximize the doping rate and resultantprocess throughput. The deposition component may be increased byselecting a dopant hydride gas rather than a fluoride, and one or moreof the following: reducing the implant RF bias voltage, reducing thedilution gas flow, increasing the process chamber pressure, reducing thewafer temperature. A typical soak anneal (anneal time of seconds to tensof seconds or longer) is sufficient to diffuse the deposited andimplanted dopant species throughout the layer thickness and activate thediffused dopant (to the solid solubility limit at the annealtemperature).

In one example of a low energy chamber seasoning process carried outprior to a plasma immersion ion implantation process using a fluoridedopant gas, the chamber seasoning process gas was the fluorocarbon gasC4F6 at a gas flow rate of 500 sccm. The ESC and chamber walltemperatures were the same as in the fluoride dopant ion implantationexamples given above, the chamber pressure was 15 mT and the sourcepower was 2000 watts applied at each reentrant conduit. The timerequired to season the chamber was about the same as the time requiredto perform the ion implantation process. In this example, the biasvoltage may be increased to 8 kV to transform the process to a highenergy process without changing the other parameters. The range ofpossible chamber pressure values in the chamber seasoning process isfrom 5 to 100 mT. The range of possible source power values in thechamber seasoning process is from 300 to 3000 Watts for each reentrantconduit. The range of gas flow rates in the chamber seasoning process is100 to 2000 sccm.

In one example of a chamber seasoning process carried out prior to aplasma immersion ion implantation process using a hydride dopant gas,the chamber seasoning process gas was the hydrocarbon gas C3H6, and theprocess parameters were the same as in the previous example, except thatthe ESC temperature was 25 degrees C., and the bias voltage was 1 kV ina low energy version of the process and 8 kV in a high energy version ofthe process.

In one example of a chamber cleaning process for removing a fluorocarbonseasoning film from the chamber interior surfaces, the external RPSchamber was used to form a plasma from a cleaning gas and furnishdissociated neutrals of that gas to the main chamber. The cleaning gasincluded 90% oxygen and 10% hydrogen, introduced into the RPS chamber ata total flow rate of 2000 sccm, the hydrogen being helpful in removingdopant residue from the main chamber interior surfaces. The main chamberwall and ESC temperatures were the same as in the above examplesinvolving fluoride chemistries, while the main chamber pressure wasabout 1 torr. The source power applied to the RPS plasma source wasabout 5000 Watts.

In one example of a cleaning process for removing a hydrocarbonseasoning film from the chamber interior surfaces using the external RPSsource, all the process parameters were the same as above except thatthe ESC temperature was 25 degrees C. and the chamber wall temperaturewas 35 degrees C.

In one example of a chamber cleaning process for removing a fluorocarbonseasoning film from the chamber interior surfaces, plasma source powerused to form a plasma from a cleaning gas within the main chamber 42.The cleaning gas included oxygen and hydrogen, each introduced into theRPS chamber 334 at a flow rate of 500 sccm, the hydrogen being helpfulin removing dopant residue from the main chamber interior surfaces. Themain chamber wall and ESC temperatures were the same as in the aboveexamples involving fluoride chemistries, while the main chamber pressurewas 15 mT. The source power was 1000 watts applied at each reentrantconduit 22 a, 22 b. Bias voltage up to about 1 kV may be added toaccelerate cleaning of the polymer from the colder ESC surface.

In one example of a cleaning process for removing a hydrocarbonseasoning film from the chamber interior surfaces using a plasma formedwithin the main chamber, all the process parameters were the same asabove except that the ESC temperature was 25 degrees C. and the chamberwall temperature was 35 degrees C.

One chamber cleaning process employing the multi-mode reactor isperformed as follows:

-   1. A cleaning gas and an optional non-reactive gas are introduced    through RPS 334.-   2. Plasma is generated within RPS 334.-   3. Plasma-generated species (which can include radicals and ions, as    well as electrons) from the RPS 334 flow into the main chamber 42    (via showerhead).-   4. A plasma is generated in the main process chamber 42 (for example    by applying RF plasma source power or RF plasma bias power).-   5. As a result the main chamber interior is cleaned. The purpose of    applying bias power in the main chamber 42 is to increase the plasma    potential (even of a weak plasma) to overcome thermal energy    threshold limitations of the chemical reaction between cleaning    species generated by the downstream source and deposited materials    to be cleaned. The weak plasma with ion energies of ˜10 eV to a few    hundred eV allow cleaning at low temperature with very low etching    of chamber and process kit materials. Contamination is prevented the    same way that has been described above using a subsequent seasoning    process.

The cleaning gas mix introduced into the RPS 334 can include one or moreof NF3, O2, H2, N2, N2O, H2O which might be combined (optionally) withinert such as He, Ne, Ar, Xe.

One process example may be as follows: NF3 gas at a flow rate of 1000sccm, O2 gas at a flow rate of 500 sccm and H2 gas at a flow rate of 100sccm are provided to the RPS, with the RPS chamber pressure being around500 mtorr to several torr (preferably 1 torr), the RPS plasma sourcepower being about 5 KW, the main chamber pressure being about 50 to 250(preferably 100) mtorr. It should be noted that the main chamber gasdistribution showerhead drops the pressure between the RPS 334 and themain chamber 42. The chamber wall/ceiling temperature is about 60degrees C., the ESC temperature is about 35 degrees C., and the biasvoltage applied to the ESC is about 100-1000V (preferably 300V). Thisprocess cleans hydrocarbon or fluorcarbon seasoning polymer as well asdeposition products of hydride or fluoride dopant and Si-baseddeposition in less time than the season time required, which istypically less time than the implant time required (e.g., 20 seconds toseason, 20 seconds to implant, and 20 second to clean the chamber).

Another process example may be as follows: NF3 gas at a flow rate of500sccm , and O2 gas at a flow rate of 100 sccm and H2 gas at a flowrate of 100 sccm are provided to the RPS, with the RPS chamber pressurebeing around 100 mtorr to about 800 mtorr (preferably about 400 mtorr),the RPS plasma source power being about 5 KW, the main chamber pressurebeing about 10 to 90 (preferably 30) mtorr. It should be noted that themain chamber gas distribution showerhead drops the pressure between theRPS 334 and the main chamber 42. The chamber wall/ceiling temperature isabout 60 degrees C., the ESC temperature about 35 degrees C., and thesource power was 1000 watts applied at each reentrant conduit 22 a, 22b. This process cleans hydrocarbon or fluorcarbon seasoning polymer aswell as deposition products of hydride or fluoride dopant and Si-baseddeposition in less time than the season time required, which istypically less time than the implant time required (e.g., 20 seconds toseason, 20 seconds to implant, and 20 second to clean the chamber) .Optionally, a bias voltage of 10-1000 volts (preferably about 100 volts)may be applied to the ESC to further reduce the cleaning time.

Another chamber cleaning process employing the multi-mode reactor in asequential manner is performed as follows:

-   1. A cleaning gas and an optional non-reactive gas are introduced    through RPS 334.-   2. Plasma is generated within RPS 334.-   3. Plasma-generated species (which can include radicals and ions, as    well as electrons) from the RPS 334 flow into the main chamber 42    (via showerhead), partially cleaning the main chamber interior    surfaces.-   4. The same or different cleaning gas and optional non-reactive gas    are introduced into the main chamber.-   5. Plasma source or bias power is applied to generate a plasma in    the main chamber, further cleaning the main chamber.-   6. The above sequence is optionally repeated until the main chamber    is clean. Alternatively the sequence of cleaning using the RPS    source and the plasma source may be reversed.

A process example of the above-described sequential cleaning process maybe as follows: First, plasma source power was used to form a plasma froma cleaning gas within the main chamber 42. The cleaning gas includedoxygen and hydrogen, each introduced into the RPS chamber 334 at flowrates of 500 and 100 sccm, respectively, the hydrogen being helpful inremoving dopant residue from the main chamber interior surfaces. Themain chamber wall and ESC temperatures were 60 and 35 degrees C.,respectively, while the main chamber pressure was 20 mT. The sourcepower was 1000 watts applied at each reentrant conduit 22 a, 22 b. Biasvoltage of about 100-1000 volt may be added to accelerate cleaning ofthe polymer from the colder ESC surface. Second, the RPS source is usedto clean the chamber surfaces in the following process: NH3 gas at aflow rate of 2000 sccm is provided to the RPS, with the RPS chamberpressure being around 500 mtorr to about 5 torr (preferably about 2torr), the RPS plasma source power being about 5 KW, the main chamberpressure being about 100 mtorr to several torr (preferably about 500mtorr). It should be noted that the main chamber gas distributionshowerhead drops the pressure between the RPS 334 and the main chamber42. The chamber wall/ceiling temperature is about 60 degrees C. and theESC temperature is about 35 degrees C. as in the foregoing examples.This sequential process cleans hydrocarbon or fluorcarbon seasoningpolymer as well as deposition products of hydride or fluoride dopant andSi-based deposition in less time than the season time required, which istypically less time than the implant time required (e.g., 20 seconds toseason, 20 seconds to implant, and 20 seconds total to clean thechamber). Optionally the sequence may be reversed.

The RPS chamber 334 produces plasma-generated species for deliverythrough the gas distribution showerhead into the main chamber 42. Theseplasma-generated species can include radicals and other excited species,and may include reactive species and/or non-reactive species.

Deposited Layer Doping:

A common doping process is the doping of a deposited layer ofsemiconductor material over a dielectric material. This structure iscommonly used in MOS transistors for example, in memory devices. Adeposited layer of amorphous or polycrystalline silicon is depositedover a thermally grown SiO2 material on a silicon substrate. The SiO2layer is the gate dielectric and the amorphous or polycrystallinesilicon layer is the gate electrode or bit line in the completedtransistor. (Note that other gate dielectrics may be used). Typically aconventional beamline implanter is used to implant boron ions (B+), forexample, to a depth within the deposited layer of amorphous orpolycrystalline silicon. The layer may be masked or unmasked, dependingon the application and process sequence. The workpiece or substrate isstripped and cleaned after implant, if necessary, then subsequentlyannealed to (1) diffuse the dopant material across the thickness of theamorphous or polycrystalline silicon deposited layer, (2) crystallizethe layer to at least a limited degree, and to (3) activate the dopant(replace silicon atoms in a crystal lattice), producing a conductivegate and/or line. Diffusion of the dopant across the thickness of thelayer to the gate interface is important, as any poorly doped regionwill yield a high series resistance. Furthermore, when the gate isbiased in actual operation with an electric field, a lower resistance atthe gate dielectric interface provides for a reduced depletion regionwidth (region of poor conductivity under high electric field). A lowseries resistance and a minimum depletion region width is required foroptimum device speed and switching performance. To achieve low seriesresistance and minimum depletion region width with the constraint thatthe implanted dose not penetrate too far, (i.e., into the gatedielectric) requires a high dopant dose at relatively low energy. (i.e.,B+, 5E15 atoms/cm2, 3 keV). Beamline implanters' productivity fall offat low energy, and the high dose requirement compounds the productivityproblem. Decelerated beams (“decel mode”) typically cannot be used toenhance productivity because energy contamination (from energeticneutral species) can penetrate the gate dielectric and adversely affectdevice performance. Implantation of molecular species such as BF2+,which yield higher beam currents, typically cannot be used to enhanceproductivity because the presence of fluorine at or near the gatedielectric may adversely affect device performance as well.

Plasma doping can be used to increase the productivity (numbers ofwafers processed per hour) of the above-described doping application.The plasma doping can be carried out in a plasma immersion ionimplantation process of the type described above in which the dopantspecies is implanted within the workpiece with a desired depth profile(i.e., within the deposited silicon layer). Preferably, however, thedoping is carried out at a lower bias voltage so that dopant speciesfrom the plasma deposit in a film formed on the surface of the depositedsilicon layer. Once a desired dose is achieved, the workpiece isannealed as described above in order to diffuse the dopant materialsthrough the entire thickness of the deposited silicon layer. Thisdiffusion ensures high dopant concentration and activation throughoutthe thickness of the deposited silicon layer, including up to thesilicon/oxide interface where it is so important to attain a low sheetresistance to minimize depletion in this region. Alternatively, the biasvoltage may be slightly increased so that, while some of the dopantmaterial is deposited on the silicon layer surface, other dopantmaterial is implanted beneath the surface at a relatively shallow depth.The reactor chamber pressure is adjusted according to whether dopantdeposition or dopant implantation is desired. Dilution gas such ashydrogen may also be added to control or reduce deposition.

Preferably, the workpiece support is an electrostatic chuck (ESC), whichis used to electrostatically attract the workpiece to the top surface ofthe ESC to facilitate heat transfer between workpiece and the ESC. TheESC is preferably temperature controlled (or is coupled to a temperaturecontrolled surface) to maintain approximately constant temperature, evenas the heat load on the workpiece (and ESC) varies with the applicationof power. The ESC may be heated or cooled. The ESC may be of theconventional type that employs a heat transfer gas between esc andworkpiece to increase the thermal coupling (heat transfer coefficient).Preferably, however, the ESC is a high contact force gasless cooling ESCof the type disclosed above with reference to FIG. 1. The workpiecetemperature is controlled through the ESC and is set below a depositionthreshold temperature (if a dopant deposition layer is desired) andabove a deposition threshold temperature (if ion implantation isdesired). The workpiece temperature (through the ESC) is preferably setbelow the etch threshold temperature (to prevent significant etching ofthe workpiece surface). For processes that use a photoresist mask, theworkpiece temperature is also maintained below a maximum temperaturelimitation of the photoresist mask.

A dopant gas (such as BF3 or B2H6) is introduced to the vacuum chamberand chamber pressure is preferably controlled to a target level. If somedeposition is desired, then preferably a hydride gas such as B2H6 isused.

Some applications may benefit from operating the workpiece at anelevated temperature to maintain deposited layer structure or morphologywhich provides for improved activation and lower resistance. Selectionof hydride dopants may provide improved (lower) resistance in suchcases.

RF power is applied to generate a plasma. RF is advantageously used (ascompared with DC or pulsed DC) because RF power will couple acrossinsulating layers on workpiece, insulating layers on the ESC, and acrossinsulating films that accumulate on chamber walls, all without asignificant voltage drop. This provides a great advantage over D.C.coupled plasma processes. Plasma generated from a DC source (includingpulsed D.C.) depends upon surface interactions with energetic ions, andtherefore D.C. coupled plasmas are susceptible to large variations asinsulating films accumulate on chamber walls. They are also susceptibleto losses across insulating layers on the workpiece and/or the ESC. Inan RF-powered plasma, plasma is generated by either an oscillating RFsheath coupling to electrons, or by directly coupling an RF electricfield to electrons. RF is also more efficient than D.C. in producingplasma, allowing operation at lower voltage and lower pressure than DCwould allow. Preferably, some (or all) of the RF power may be applied asbias power through the ESC. Alternatively or additionally, some of theRF power may be applied as plasma source power.

P-N Junction formation:

For forming P-N junctions, such as the source or drain contact orextensions of a MOSFET used in a logic device, ion implantation ispreferred (rather than dopant deposition and subsequent diffusion orannealing). This is because the highly abrupt and extremely shallowjunction profile required for MOSFET source and drain extensions canbest be attained by implanting dopant species with a depth profilecorresponding to the depth of the desired junction, and then minimizing(or nearly preventing) any diffusion during the subsequent dopantactivation anneal step. Ideally a diffusionless anneal such as laseranneal is used, but other anneal processes such as spike anneals can beused as well. In the case where a spike anneal is used (notdiffusionless), the dopant species are implanted with a depth profilecorresponding to a depth selected to be less than the desired finaljunction depth, such that the final spike annealed junction will havethe requisite depth. Preamorphizing the region to be implanted prior todopant implantation may be performed to maximize junction abruptness.

Such a plasma immersion ion implantation process has been described indetail in the related Pat. applications referenced above.

Fluoride or hydride dopant gases may be used to form p-n junctions in aplasma immersion ion implantation process.

Pressure may be selected to be lower to minimize angular distribution ofion velocities for a non-conformal or less conformal implant profile, orhigher to maximize angular distribution of ion velocities for a moreconformal implant profile, such as for implanting three dimensionalstructures (ie. FIN-FET transistors).

RF power is advantageously used to generate the plasma for the samereasons described above.

Briefly, such processes maintain the workpiece temperature (through theESC) above the deposition threshold temperature (to prevent significantdeposition on the workpiece surface during ion implantation) whileapplying sufficient bias power to set the ion implant depth to thedesired junction depth. Such processes preferably also maintain theworkpiece temperature (through the ESC) below the etch thresholdtemperature (to prevent significant etching of the workpiece surfaceduring ion implantation) while applying sufficient bias power to set theion implant depth to the desired junction depth. For high doseimplantation it is important to prevent excessive etch loss because suchloss can limit the maximum possible dose attainable. For implantprocesses that use a photoresist mask, the workpiece temperature is alsomaintained below a maximum temperature limitation of the photoresistmask. Some applications may benefit from operating the workpiece atsufficiently high temperature to reduce amorphization (above 100 degreeC.) or maintain crystallinity (above 500-600 degree C.) while performingimplantation. Selection of hydride dopants may provide improved sheetresistance at the requisite junction depth in such cases.

The ESC therefore can serve both as the agent for controlling theworkpiece temperature and as the RF power applicator for RF bias powerapplied to the workpiece and coupled to the plasma.

In addition to deposited layer doping and P-N junction formation, otherapplications may benefit from utilizing the ESC as the agent forcontrolling the workpiece temperature and as the RF power applicator forRF bias power applied to the workpiece and coupled to the plasma.Surface modification processes such as implantation or nitridation ofgate dielectric materials, work function modification of metal gatematerials by implantation, and surface cleaning with hydrogen areexamples where workpiece temperature must be controlled while modifyingthe workpiece suface by plasma ion bombardment.

In the foregoing description of the RPS 334, the term “excited neutrals”refers to products of the RPS that include uncharged atoms or moleculesthat have a higher internal energy (i.e., higher than the “ground state”for that specie) attributable to, for example, an inelastic collisionwith another particle (typically an energetic electron) or due toabsorption of a photon of sufficient energy. The excited state may bestable or metastable (short-lived) before relaxing to a lower energystate and emitting a photon. Inelastic collisions between electrons andneutrals or ions can result in excitation reactions, dissociationreactions and ionization reactions (including dissociative ionizationreactions).

In some applications, the bias voltage required may be relatively high,as is the case in plasma immersion ion implantation processes for arelatively deep implant depth. In such cases, it is difficult to attaina low implant dosage because the dose rate is so high. If a lowaccurately defined dosage is required in such a process, then the doserate is preferably reduced by pulsing the applied RF power at a pulserate and duty cycle that produces a desirably reduced implant dose rate.This approach is particularly simple and effective if the only (or thepredominant) plasma-generating power is a plasma RF bias generatorcoupled to the wafer support pedestal, since only this single RFgenerator needs to be pulsed in order to attain a desirably reducedimplant dose rate.

While the invention has been described in detail by specific referenceto preferred embodiments, it is understood that variations andmodifications thereof may be made without departing from the true spiritand scope of the invention.

1. A method of processing a workpiece, comprising: providing a mainreactor chamber having a ceiling gas distribution plate facing a wafersupport and side gas injectors below said gas distribution plate, andproviding a remote source chamber enclosed separately from the mainreactor chamber; evacuating said main reactor chamber and evacuatingsaid remote source chamber; placing a wafer on said wafer support insaid main chamber and, while said wafer is on said wafer support,providing a plasma in said main chamber having ions that impinge on saidwafer by introducing a process gas through said side gas injectors insaid main reactor chamber and applying RF power to external transversereentrant conduits having chamber entry ports on opposite sides of saidmain reactor chamber, so as to produce an oscillating plasma current ina closed reentrant path that encircles said gas distribution plate;increasing dissociation of species in said main reactor chamberindependently of said RF power, by generating a remote plasma in saidremote source chamber and introducing through said ceiling gasdistribution plate excited radicals from said remote plasma into saidmain reactor chamber.
 2. The method of claim 1 further comprising: priorto placing the wafer on the support, depositing a seasoning film oninterior surfaces of said main reactor chamber by generating anseasoning oscillating plasma current in said closed reentrant path witha seasoning species gas.
 3. The method of claim 2 further comprising:after placing the wafer on said wafer support but before generating theplasma of reactive species in said main reactor chamber, performing awafer clean step by generating a plasma of wafer cleaning species insaid remote source chamber and introducing radicals of the wafercleaning species from the remote source chamber into the main chamber toclean undesired materials from said wafer.
 4. The method of claim 3further comprising: generating the plasma of reactive species in saidmain reactor chamber within a sufficiently short time followingcompletion of said wafer clean step to prevent re-growth of native oxideon said wafer.
 5. The method of claim 1 further comprising: coupling RFbias power to the wafer of a sufficient power level to perform plasmaimmersion ion implantation of a species derived from said process gas toa desired implant depth.
 6. The method of claim 5 further comprising:controlling the temperature of the wafer by clamping the wafer to thewafer support by generating an electrostatic wafer clamping force in thewafer support, and regulating the temperature of the wafer by regulatingthe electrostatic wafer clamping force.
 7. The method of claim 6 furthercomprising: providing a polished continuous wafer support surface onsaid wafer support uninterrupted by open channels; prior to placing thewafer on the wafer support, depositing a cushioning layer on said wafersupport surface.
 8. The method of claim 7 wherein depositing acushioning layer is performed while maintaining the wafer supportsurface at a temperature conducive for deposition of said cushioningfilm, so as to deposit said cushioning film on said wafer supportsurface and not on other interior surfaces of said main chamber.
 9. Themethod of claim 2 further comprising: during the deposition of theseasoning film, maintaining the interior surfaces of said main chamberat a temperature conducive for depositing said seasoning film;depositing a cushioning layer on a wafer support surface of said wafersupport while maintaining a wafer support surface of said wafer supportat a temperature conducive for deposition of said cushioning film, so asto deposit said cushioning film on said wafer support surface and not onother interior surfaces of said main chamber.
 10. A method of processinga workpiece, comprising: providing a main reactor chamber having aceiling gas distribution plate facing a wafer support and side gasinjectors below said gas distribution plate, and providing a remotesource chamber enclosed separately from the main reactor chamber;evacuating said main reactor chamber and evacuating said remote sourcechamber; placing a wafer on said wafer support in said main chamber and,while said wafer is on said wafer support, generating a plasma in saidmain chamber having ions that impinge on said wafer by introducing aprocess gas through said side gas injectors in said main reactor chamberand applying RF power to external transverse reentrant conduits havingchamber entry ports on opposite sides of said main reactor chamber, soas to produce an oscillating plasma current in a closed reentrant paththat encircles said gas distribution plate; regulating the proportion ofreactive ions to reactive radicals independently of said RE power, bygenerating a remote plasma in said remote source chamber and introducingthrough said ceiling gas distribution plate reactive radicals from saidremote plasma into said main reactor chamber.
 11. The method of claim 10further comprising: prior to placing the wafer on the support,depositing a seasoning film on interior surfaces of said main reactorchamber by generating an seasoning oscillating plasma current in saidclosed reentrant path with a seasoning species gas.
 12. The method ofclaim 11 further comprising: after placing the wafer on said wafersupport but before generating the plasma of reactive species in saidmain reactor chamber, performing a wafer clean step by generating aplasma of wafer cleaning species in said remote source chamber andintroducing radicals of the wafer cleaning species from the remotesource chamber into the main chamber to clean undesired materials fromsaid wafer.
 13. The method of claim 12 further comprising: generatingthe plasma of reactive species in said main reactor chamber within asufficiently short time following completion of said wafer clean step toprevent re-growth of native oxide on said wafer.
 14. The method of claim10 further comprising: coupling RF bias power to the wafer of asufficient power level to perform plasma immersion ion implantation of aspecies derived from said process gas to a desired implant depth. 15.The method of claim 14 further comprising: controlling the temperatureof the wafer by clamping the wafer to the wafer support by generating anelectrostatic wafer clamping force in the wafer support, and regulatingthe temperature of the wafer by regulating the electrostatic waferclamping force.
 16. The method of claim 15 further comprising: providinga polished continuous wafer support surface on said wafer supportuninterrupted by open channels; prior to placing the wafer on the wafersupport, depositing a cushioning layer on said wafer support surface.17. The method of claim 16 wherein depositing a cushioning layer isperformed while maintaining the wafer support surface at a temperatureconducive for deposition of said cushioning film, so as to deposit saidcushioning film on said wafer support surface and not on other interiorsurfaces of said main chamber.
 18. The method of claim 11 furthercomprising: during the deposition of the seasoning film, maintaining theinterior surfaces of said main chamber at a temperature conducive fordepositing said seasoning film; depositing a cushioning layer on a wafersupport surface of said wafer support while maintaining a wafer supportsurface of said wafer support at a temperature conducive for depositionof said cushioning film, so as to deposit said cushioning film on saidwafer support surface and not on other interior surfaces of said mainchamber.